git clean がかなり便利です。
git clean -f で簡単に削除できます。
$ git clean -h
usage: git clean [-d] [-f] [-i] [-n] [-q] [-e <pattern>] [-x | -X] [--] <paths>...
-q, --quiet do not print names of files removed
-n, --dry-run dry run
-f, --force force
-i, --interactive interactive cleaning
-d remove whole directories
-e, --exclude <pattern>
add <pattern> to ignore rules
-x remove ignored files, too
-X remove only ignored files
console
$ git clean -f