Replace 'git whatchanged' with 'git log --stat'

[Bill-Sommerfeld]

The git whatchanged command is deprecated in git 2.51.0; recent git documentation suggests using git log --raw --no-merges instead.

I brought this up on IRC; rough consensus among advocates on IRC was that we should no longer require this for changes via Gerrit; additionally, several advocates suggested that git log --stat output was more useful than --raw.