test: Remove raw-tx byte juggling in mempool_reorg
test: Remove raw-tx byte juggling in mempool_reorg

Summary: This is a backport of Core [[https://github.com/bitcoin/bitcoin/pull/18770 | PR18770]]

Test Plan: `./test/functional/test_runner.py mempool_reorg`

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8989

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