apparmor: remove minimum size check for vmalloc()

This is a follow-up to commit b5b3ee6c

 "apparmor: no need to delay vfree()".

Since vmalloc() will do "size = PAGE_ALIGN(size);",
we don't need to check for "size >= sizeof(struct work_struct)".

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: John Johansen <john.johansen@canonical.com>