populate_db: Remove unnecessary pre-population of URL cache.

76deb30312 changed this to not just be the URL, but rather a
prefixed hash of the URL, but failed to update this location which
wrote to it.  This meant that this pre-population step was writing to
the wrong keys in the durable cache, and thus ineffective.

Then, da33b72848 switched the cache to be in-memory, making this
write to the wrong keys in an in-process memory store.  There is no
way to pre-fill this sort of cache, except at server start-up.

Finally, and most fundamentally, 8c0c9ca7a4 then disabled
`inline_url_embed_preview` by default, making the code entirely moot.

Remove the triply-unnecessary code.

zerver/tests/fixtures/docs_url_preview_data.json

@@ -1,26 +0,0 @@
-{
-    "https://zulip.readthedocs.io/en/latest/subsystems/analytics.html": {
-        "description": "Zulip has a cool analytics system for tracking various useful statistics\nthat currently power the /stats page, and over time will power other\nfeatures, like showing usage statistics for the various streams. It is\ndesigned around the following goals:",
-        "title": "Analytics — Zulip 1.7.1+git documentation"
-    },
-    "https://zulip.readthedocs.io/en/latest/subsystems/client.html": {
-        "description": "zerver.models.Client is Zulip analogue of the HTTP User-Agent\nheader (and is populated from User-Agent).  It exists for use in\nanalytics and other places to provide human-readable summary data\nabout which Zulip client was used for an operation (e.g. was it the\nAndroid app, the desktop app, or a bot?).",
-        "title": "Clients in Zulip — Zulip 1.7.1+git documentation"
-    },
-    "https://zulip.readthedocs.io/en/latest/subsystems/emoji.html": {
-        "description": "Emoji seem like a simple idea, but there actually a ton of\ncomplexity that goes into an effective emoji implementation.  This\ndocument discusses a number of these issues.",
-        "title": "Emoji — Zulip 1.7.1+git documentation"
-    },
-    "https://zulip.readthedocs.io/en/latest/subsystems/full-text-search.html": {
-        "description": "Zulip supports full-text search, which can be combined arbitrarily\nwith Zulip full suite of narrowing operators.  By default, it only\nsupports English text, but there is an experimental\nPGroonga integration that provides\nfull-text search for all languages.",
-        "title": "Full-text search — Zulip 1.7.1+git documentation"
-    },
-    "https://zulip.readthedocs.io/en/latest/subsystems/logging.html": {
-        "description": "Having a good system for logging error reporting is essential to\nmaking a large project like Zulip successful.  Without reliable error\nreporting, one has to rely solely on bug reports from users in order\nto produce a working product.",
-        "title": "Logging and Error reporting — Zulip 1.7.1+git documentation"
-    },
-    "https://zulip.readthedocs.io/en/latest/translating/translating.html": {
-        "description": "To make Zulip even better for users around the world, the Zulip UI is\nbeing translated into a number of major languages, including Spanish,\nGerman, Hindi, French, Chinese, Russian, and Japanese, with varying levels of\nprogress. If you speak a language other than English, your help with\ntranslating Zulip would be greatly appreciated!",
-        "title": "Translation guidelines — Zulip 1.7.1+git documentation"
-    }
-}

zilencer/management/commands/populate_db.py

@@ -28,7 +28,6 @@ from zerver.actions.message_send import build_message_send_dict, do_send_message
 from zerver.actions.realm_emoji import check_add_realm_emoji
 from zerver.actions.users import do_change_user_role
 from zerver.lib.bulk_create import bulk_create_streams
-from zerver.lib.cache import cache_set
 from zerver.lib.generate_test_data import create_test_data, generate_topics
 from zerver.lib.onboarding import create_if_missing_realm_internal_bots
 from zerver.lib.push_notifications import logger as push_notifications_logger
@@ -36,7 +35,6 @@ from zerver.lib.server_initialization import create_internal_realm, create_users
 from zerver.lib.storage import static_path
 from zerver.lib.stream_color import STREAM_ASSIGNMENT_COLORS
 from zerver.lib.types import ProfileFieldData
-from zerver.lib.url_preview.preview import CACHE_NAME as PREVIEW_CACHE_NAME
 from zerver.lib.user_groups import create_user_group
 from zerver.lib.users import add_service
 from zerver.lib.utils import generate_api_key
@@ -810,15 +808,6 @@ class Command(BaseCommand):
         # Generate a new set of test data.
         create_test_data()
 
-        # prepopulate the URL preview/embed data for the links present
-        # in the config.generate_data.json data set.  This makes it
-        # possible for populate_db to run happily without Internet
-        # access.
-        with open("zerver/tests/fixtures/docs_url_preview_data.json", "rb") as f:
-            urls_with_preview_data = orjson.loads(f.read())
-            for url in urls_with_preview_data:
-                cache_set(url, urls_with_preview_data[url], PREVIEW_CACHE_NAME)
-
         if options["delete"]:
             if options["test_suite"]:
                 # Create test users; the MIT ones are needed to test