#138435 was an attempt to fix the issue in #138168 where the Smooth
Operator modifies locked vertex groups. Unfortunately, the fix actually
changed some already-correct code to be incorrect to compensate for the
buggy code in the Smooth Operator.
This reverts that fix and applies a correct fix, which is to exclude
locked vertex groups in the Smooth Operator's code itself.
Pull Request: https://projects.blender.org/blender/blender/pulls/141093
2630fc4978