git rev-list master | while read rev; do git ls-tree -lr $rev | cut -c54- | sed -r 's/^ +//g;'; done | sort -u | sort -rnk1 | head -n 20
replace DUMBFILE
git filter-branch --tag-name-filter cat --index-filter 'git rm -r --cached --ignore-unmatch DUMBFILE' --prune-empty -f -- --all