Summary:
Fix the build failure caused by D41998.

https://phorge.dev.yugabyte.com/D40891 removed the function `CommitTransactionScopedSessionState` that I was using and was landed after I triggered Jenkins, but 1 hour before my revision was landed. So I guess it was missed due to that.

Please ignore the code duplication between CommitPlainTransaction and CommitPlainTransactionContainingDDL functions. I have the revision D42485 ready to
refactor that logic. This is a quick fix just for the build.

Test Plan: Jenkins:urgent,compile only

Reviewers: myang, aagrawal, skumar, kramanathan

Reviewed By: aagrawal, kramanathan

Subscribers: kramanathan, yql

Differential Revision: https://phorge.dev.yugabyte.com/D42489