[ubsan] tentatively remove suppressions for txmempool and serialize

Summary: If we never see any failure it will be much harder to fix the problem, and file-wide suppressions can hide introduction of new problems.

Test Plan:
With UBSAN
ninja && ninja check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12830