Sanity-check script sizes in bitcoin-tx

Summary:
"Sanity-check script sizes in bitcoin-tx (Matt Corallo)"

This is a backport from Core PR11554: https://github.com/bitcoin/bitcoin/pull/11554

Test Plan:

ninja check
./test/functional/test_runner.py

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4666