Summary:
Revision https://phorge.dev.yugabyte.com/D40932 introduced a field `bool needs_pg_session_transaction = 25` in message `PgPerformOptionsPB` for performing session advisory lock requests. Since session advisory lock requests don't need any metadata corresponding to the ongoing regular/plain transaction, this isn't the right place to introduce any fields required for session advisory locks.

This diff removes the previously added field, and uses the field `bool session` in `PgAcquireAdvisoryLockRequestPB` to infer whether the advisory lock request arriving at `pg_client_session` is a transactional advisory lock or a session advisory lock.

Note: Since rpcs involving usage of `PgPerformOptionsPB` seem to be for local node communication only, it is safe to remove the field.
Jira: DB-14844

Test Plan: Jenkins

Reviewers: dmitry, esheng, yyan

Reviewed By: dmitry

Subscribers: ybase, yql

Differential Revision: https://phorge.dev.yugabyte.com/D41168