WL#12212: Remove metadata_locks_hash_instances and metadata_locks_cache_size System Variables

Affects: Server-8.0   —   Status: Complete   —   Priority: Medium

In MySQL 5.7.4, metadata locking implementation changes made the 
metadata_locks_hash_instances and metadata_locks_cache_size system variables 
unnecessary, so they became deprecated.

The current task is to remove metadata_locks_hash_instances and 
metadata_locks_cache_size in MySQL 8.0.