[refactor] Update some comments in validation.cpp as we arent doing DoS there
Summary: This is a backport of Core PR15141 : https://github.com/bitcoin/bitcoin/pull/15141/commits/2120c31521aa51aa1984ee33250b8320506d3a0f
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Differential Revision: https://reviews.bitcoinabc.org/D6738