Remove ActiveRecord::Transactions#rollback_active_record_state!

`rollback_active_record_state!` was removed from `save!` but not `save`
in da840d13da. I believe that leaving it
in `save` was a mistake, since that commit was intended to move the
rollback logic from the `save`/`save!` call to the transaction stack.

As of 67d8bb963d the record's original
state is lazily restored the first time it's accessed after the
transaction, instead of when a rollback occurs. This means that the call
to `restore_transaction_record_state` here has no effect: the record's
transaction level is incremented twice (in rollback_active_record_state!
and `with_transaction_returning_status`), isn't decremented again until
the the `ensure` block runs, and won't hit zero until the next time
`sync_with_transaction_state` is called.

activerecord/lib/active_record/transactions.rb

@@ -306,9 +306,7 @@ module ActiveRecord
     end
 
     def save(*) #:nodoc:
-      rollback_active_record_state! do
-        with_transaction_returning_status { super }
-      end
+      with_transaction_returning_status { super }
     end
 
     def save!(*) #:nodoc:
@@ -319,17 +317,6 @@ module ActiveRecord
       with_transaction_returning_status { super }
     end
 
-    # Reset id and @new_record if the transaction rolls back.
-    def rollback_active_record_state!
-      remember_transaction_record_state
-      yield
-    rescue Exception
-      restore_transaction_record_state
-      raise
-    ensure
-      clear_transaction_record_state
-    end
-
     def before_committed! # :nodoc:
       _run_before_commit_without_transaction_enrollment_callbacks
       _run_before_commit_callbacks