Drop UpdateTransaction in favor of UpdateInput

Summary:
Updating the input explicitly requires the caller to present a mutable
input, which more clearly communicates the effects and intent of the method.

In most cases, this input is already immediately available and need not be
looked up.

This is a backport of Core PR13269

Depends on D4200

Test Plan:

make check
./test/functional/test_runner.py

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4203