Rename SCRIPT_ENABLE_CHECKDATASIG to SCRIPT_VERIFY_CHECKDATASIG_SIGOPS.

Summary:
The new name is more descriptive of what the flag actually does.

This is a straight rename with no other changes.

Test Plan: make check

Reviewers: deadalnix, markblundeberg, #bitcoin_abc

Reviewed By: deadalnix, #bitcoin_abc

Maniphest Tasks: T653

Differential Revision: https://reviews.bitcoinabc.org/D3112