Remove duplicate query logging that breaks Django's assertNumQueries (#4367)

* Remove duplicate query logging that breaks Django's assertNumQueries

The SqlCommenter _QueryWrapper manually appends the SQL string to
queries_log when a CursorDebugWrapper is active. However,
CursorDebugWrapper.debug_sql already logs the query as a dict with
"sql" and "time" keys. This causes two problems:

1. Queries are double-counted in queries_log
2. The raw string entries cause a TypeError in Django's
   assertNumQueries, which expects dict entries with a "sql" key

Remove the manual append and let Django handle query logging.

* Remove outdated comment about MySQL

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Co-authored-by: Leighton Chen <lechen@microsoft.com>