apparmor: remove useless static inline functions

Remove the following useless static inline functions:

1. label_is_visible() is a static function in
security/apparmor/label.c, and it's not used, aa_ns_visible()
can do the same things as it, so it's redundant.

2. is_deleted() is a static function in security/apparmor/file.c,
and it's not used since commit aebd873e ("apparmor: refactor
path name lookup and permission checks around labels"), so it's
redundant.

They are redundant, so remove them.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>