Merge #13633: Drop dead code from Stacks

Summary:
5617840392dad8c00c0e4216f1a536daaa9dd4bd Drop dead code from Stacks (Ben Woosley)

Pull request description:

Stacks is local to this file, and only used in DataFromTransaction, so
it's easy to confirm this code is unused.

Tree-SHA512: cc680c99f9b31cb56db70f453087d642f83906ce594c07a6bf3e61427cfbee41441495d440b240419ba3386582cf0670c0999b2f51e7fd56b00e0a0f3f618845

Backport of Core PR13633
https://github.com/bitcoin/bitcoin/pull/13633/

Test Plan:

make check

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

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4726