git-filter-branch is discouraged

mrhlpr is broken for me on newer Git versions because git prints this warning in the git filter-branch call:

$ git filter-branch
WARNING: git-filter-branch has a glut of gotchas generating mangled history
         rewrites.  Hit Ctrl-C before proceeding to abort, then use an
         alternative filtering tool such as 'git filter-repo'
         (https://github.com/newren/git-filter-repo/) instead.  See the
         filter-branch manual page for more details; to squelch this warning,
         set FILTER_BRANCH_SQUELCH_WARNING=1.

This warning isn't visible when running mrhlpr, so it just seemingly "freezes". Setting the environment variable allows it to work normally.

Should we replace it with git-filter-repo or something different? Or maybe just set the environment variable for our purposes (seems like git-filter-repo is not integrated into Git...)