[verify after deploy] Fix API endpoint docs.

After deploying to both staging and prod, double check the docs
are correct here.  This fixes the API docs on prod, which had
"POST /api/v1/messages", despite "/api" not being part of the
prod path.  Prod docs are here:

https://zulip.com/api/endpoints/

(imported from commit a2c4d316128f88171f4a76074314be64d9bc9728)

templates/zerver/api_content.json

@@ -1,7 +1,7 @@
 [
     {
         "method": "POST",
-        "endpoint": "/api/v1/messages",
+        "endpoint": "messages",
         "example_response": "{'msg': '', 'result': 'success', 'id': 12345678}",
         "returns": [
             [
@@ -35,7 +35,7 @@
     },
     {
         "method": "POST",
-        "endpoint": "/api/v1/register",
+        "endpoint": "register",
         "example_response": "{'msg': '', 'last_event_id': -1, 'result': 'success', 'queue_id': '1375801870:2942'}",
         "returns": [
             [
@@ -65,7 +65,7 @@
     },
     {
         "method": "GET",
-        "endpoint": "/api/v1/events",
+        "endpoint": "events",
         "example_response":
 "{'result': 'success',
  'msg': '',

zerver/views/__init__.py

@@ -485,6 +485,7 @@ def api_endpoint_docs(request):
     calls = ujson.loads(raw_calls)
     langs = set()
     for call in calls:
+        call["endpoint"] = "%s/v1/%s" % (settings.EXTERNAL_API_URI, call["endpoint"])
         call["example_request"]["curl"] = call["example_request"]["curl"].replace("https://api.zulip.com", settings.EXTERNAL_API_URI)
         response = call['example_response']
         if not '\n' in response: