checkpatch: remove obsolete CONFIG_EXPERIMENTAL checks

checkpatch: remove obsolete CONFIG_EXPERIMENTAL checks

Config EXPERIMENTAL has been removed from kernel in 2013 (see commit
3d374d09f16f: "final removal of CONFIG_EXPERIMENTAL"), there is no any
reason to do these checks now.

Link: http://lkml.kernel.org/r/1488234097-20119-1-git-send-email-ruslan.bilovol@gmail.com
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>