[validation] Remove unused cacheSigStore from CheckInputsFromMempoolAndCache
[validation] Remove unused cacheSigStore from CheckInputsFromMempoolAndCache

CheckInputsFromMempoolAndCache() is only called in one place, and
cacheSigStore is set to true in that call site. Remove the argument
entirely.

Also improve commenting.


Former-commit-id: 0aded415043cd1dc3d6b0bdc62239cb9fd8a51a0
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin