Revert "tests: skip test-commit-sign.sh when not root"

This reverts commit d3545b0661. Since the
test is now using the temporary copy of the gpg homedir, it is no longer
owned by root.

tests/test-commit-sign.sh

@@ -23,12 +23,6 @@ if ! ${CMD_PREFIX} ostree --version | grep -q -e '\+gpgme'; then
     exit 77
 fi
 
-# Skip the test when non-root as gpgme would not read files owned by
-# another user.
-if test "$(id -u)" != "0"; then
-    exit 77
-fi
-
 . $(dirname $0)/libtest.sh
 
 keyid="472CDAFA"