Rename the remaining sigOps to sigChecks

Summary:
Similar to D12787, the only remaining sigOps are from the options and RPCs in order to not break compatibility.

Depends on D12787.

Test Plan:

ninja all check-all
ninja bitcoin-fuzzers

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D12790