scripted-diff: validation: rename mandatory errors into block errors

Using "block" or "mempool" as the prefix in place of "mandatory" or "non-mandatory" is clearer
to a user. "non-mandatory" was renamed into "mempool" as part of #33050. This takes care of the
other half of this renaming as a scripted diff.

-BEGIN VERIFY SCRIPT-
sed -i 's/mandatory-script-verify/block-script-verify/g' $(git grep -l mandatory-script-verify)
-END VERIFY SCRIPT-

test/functional/feature_block.py

@@ -191,7 +191,7 @@ class FullBlockTest(BitcoinTestFramework):
             badblock = self.update_block(blockname, [badtx])
             reject_reason = (template.block_reject_reason or template.reject_reason)
             if reject_reason.startswith("mempool-script-verify-flag-failed"):
-                reject_reason = "mandatory-script-verify-flag-failed" + reject_reason[33:]
+                reject_reason = "block-script-verify-flag-failed" + reject_reason[33:]
             self.send_blocks(
                 [badblock], success=False,
                 reject_reason=reject_reason,