L::Util: Use autodie where applicable

Signed-off-by: Niels Thykier <niels@thykier.net>
checks/*: Remove unused arguments for "file is utf8"

L::Util's file_is_encoded_in_non_utf8 now only takes a single
argument, so update callers accordingly.

Signed-off-by: Niels Thykier <niels@thykier.net>