lint: disable check for enum type mismatch in switch statement

This check has been too quick and broke the lint build.  Among others,
lib/libpuffs has -w included in LINTFLAGS, which means that the build
can fail even for new warnings, not only for errors.

libpuffs compares a uint16_t with constants from an unnamed enum type.
Since the enum type is completely unnamed (neither a tag nor a typedef),
there is no way to define a struct member having this type. This was a
scenario that I just didn't consider when I added the check to lint.

For now, disable the new check completely.  The previously existing lint
checks stay enabled, including the one that warns about mismatched
anonymous enum types in the '==' operator, which is very similar to the
now disabled check.

(rillig)