mypy: Remove type ignores for python 3 stubs now present in typeshed.

Namely:
* posix stubs
* readfp stub

scripts/lib/email-mirror-postfix

@@ -85,7 +85,7 @@ def process_response_error(e):
         response_content = e.read()
         response_data = json.loads(response_content.decode('utf8'))
         print(response_data['msg'])
-        exit(posix.EX_NOUSER)  # type: ignore # There are no stubs for posix in python 3
+        exit(posix.EX_NOUSER)
     else:
         print("4.4.2 Connection dropped: Internal server error.")
         exit(1)
@@ -95,12 +95,12 @@ def send_email_mirror(rcpt_to, shared_secret, host, url, test, verify_ssl):
     # type: (str, str, str, str, bool, bool) -> None
     if not rcpt_to:
         print("5.1.1 Bad destination mailbox address: No missed message email address.")
-        exit(posix.EX_NOUSER)  # type: ignore # There are no stubs for posix in python 3
+        exit(posix.EX_NOUSER)
     msg_text = sys.stdin.read(MAX_ALLOWED_PAYLOAD + 1)
     if len(msg_text) > MAX_ALLOWED_PAYLOAD:
         # We're not at EOF, reject large mail.
         print("5.3.4 Message too big for system: Max size is 25MiB")
-        exit(posix.EX_DATAERR)  # type: ignore # There are no stubs for posix in python 3
+        exit(posix.EX_DATAERR)
 
     secrets_file = RawConfigParser()
     secrets_file.read("/etc/zulip/zulip-secrets.conf")

zerver/lib/bot_config.py

@@ -66,7 +66,7 @@ def load_bot_config_template(bot: str) -> Dict[str, str]:
     if os.path.isfile(config_path):
         config = configparser.ConfigParser()
         with open(config_path) as conf:
-            config.readfp(conf)  # type: ignore # readfp->read_file in python 3, so not in stubs
+            config.readfp(conf)
         return dict(config.items(bot))
     else:
         return dict()