logging: Reduce create_logger to new log_to_file.

The name `create_logger` suggests something much bigger than what this
function actually does -- the logger doesn't any more or less exist
after the function is called than before.  Its one real function is to
send logs to a specific file.

So, pull out that logic to an appropriately-named function just for
it.  We already use `logging.getLogger` in a number of places to
simply get a logger by name, and the old `create_logger` callsites can
do the same.

zerver/management/commands/sync_ldap_user_data.py

@@ -1,16 +1,18 @@
 
+import logging
 from typing import Any
 
 from django.conf import settings
 from django.core.management.base import BaseCommand
 from django.db.utils import IntegrityError
 
-from zerver.lib.logging_util import create_logger
+from zerver.lib.logging_util import log_to_file
 from zerver.models import UserProfile
 from zproject.backends import ZulipLDAPUserPopulator
 
 ## Setup ##
-logger = create_logger(__name__, settings.LDAP_SYNC_LOG_PATH)
+logger = logging.getLogger(__name__)
+log_to_file(logger, settings.LDAP_SYNC_LOG_PATH)
 
 # Run this on a cronjob to pick up on name changes.
 def sync_ldap_user_data() -> None: