Deprecate CheckFinalTx in favor of ContextualCheckTransactionForCurrentBlock

Summary:
It is somewhat more cumbersome to use, but we need a place to add the OP_RETURN replay feature.

In order to limit the size of this diff, I created a CheckFinalTx wrapper for the wallet to use. This code can be migrated later on.

Test Plan:

make check

Reviewers: freetrader, sickpig, #bitcoin_abc, kyuupichan

Reviewed By: #bitcoin_abc, kyuupichan

Subscribers: kyuupichan

Differential Revision: https://reviews.bitcoinabc.org/D144