[mempool] Don't throw expected error message when upgrading

Summary:
mempool.dat now contains unbroadcast transactions, that did not exist in
mempool.dat files created in previous version.
This commit prevent an uneccessary error message to be logged when users
update from v0.22.11 or lower.
The try..catch can be removed after everyone has upgraded to > v0.22.11.

This is a backport of Core PR18807 [4/9]
https://github.com/bitcoin/bitcoin/pull/18807/commits/9c8a55d9cb0ec73f10b196e79b637aa601c0a6b7

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9031