Merge #12996: tests: Remove redundant bytes(…) calls

Summary:
9db48c5634 tests: Remove redundant bytes² (practicalswift)

Pull request description:

This is a follow-up to #12993. As @jnewbery noted `bytes()` is idempotent.

Tree-SHA512: 0eb25e0c2c46f9abaac30f964c5eb422bece1414c840a717d86794424294cb19d995a6db7c8df2a2f4ec84776b05274a637f2c111738f397051f510e57184752

Backport of Core PR12996
https://github.com/bitcoin/bitcoin/pull/12996/

Test Plan:

make check
test_runner.py

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

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3857