Deduplicate call to PreChecks in AcceptSingleTransaction

Summary: I accidentaly duplicated this in D12347, which caused a double count of the number of ancestors.

Test Plan:
ninja check-functional-extended

mempool_updatefromblock.py is the test that highlighted the mistake

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12353