Debug Info: Remove unnecessary check for dependent array types

This was added, untested (though the relevant crash was tested), in
r128725/PR9600. Removing it doesn't cause failures & nothing I can
imagine could cause this check to ever return 'true' (we should never be
dealing with dependent types here). The subsequent change to check
"isIncompleteType" (r128855/PR9608) makes a lot more sense.