settings: Clean up pika logging.

It appears that a recent pika release started logging spammy INFO
output on the pika.connection and pika.channel channels, in addition
to the existing pika.adapters channel.

It's probably best to just move to WARNING-level logging for all of these.

This significantly cleans up the output when run-dev.py restarts
services due to a code change in the development environment.

zproject/settings.py

@@ -850,7 +850,7 @@ LOGGING: Dict[str, Any] = {
             'handlers': ['console', 'ldap_file', 'errors_file'],
             'propagate': False,
         },
-        'pika.adapters': {
+        'pika': {
             # pika is super chatty on INFO.
             'level': 'WARNING',
             # pika spews a lot of ERROR logs when a connection fails.
@@ -859,11 +859,6 @@ LOGGING: Dict[str, Any] = {
             'handlers': ['console', 'file', 'errors_file'],
             'propagate': False,
         },
-        'pika.connection': {
-            # Leave `zulip_admins` out of the handlers.  See pika.adapters above.
-            'handlers': ['console', 'file', 'errors_file'],
-            'propagate': False,
-        },
         'requests': {
             'level': 'WARNING',
         },