Small refactoring on clear_transaction_record_state

Make sure when we clean the `@_start_transaction_state` var we do it in
the same code-path.
Also this makes `clear_transaction_record_state`, more consistent with `restore_transaction_record_state`
Clear transaction state if callback raise rollback
Remove code related to adapter which are no longer in repo

As we have remove code for these adapters so no need to have tasks
Merge pull request #15131 from arunagw/aa-cleanup-rakefile

Remove code related to adapter which are no longer in repo
Merge pull request #15125 from arthurnn/small_refactoring_transaction_clear

Small refactoring on clear_transaction_record_state
Add a specific method to force the transaction record state clear

We are using that code path in only one place so we should not add a
conditional to all the other cases. This will avoid performance
regressions on the old paths.
Missed if :bomb:
Reuse the force_clear_transaction_record_state
prepend mutates the string so we can remove the assignment
Remove the assignment for real this time.

cc:
https://github.com/rails/rails/commit/a11e2fcff8cdc9691b977d8330abe63024f8c732#commitcomment-6353614
and 0369dbf
Merge pull request #15139 from zzak/habtm_build_model_name

Remove the assignment for real this time.
Remove unecessary require
Merge pull request #15140 from arthurnn/small_cleanup

Remove unecessary require