Kconfig: remove top level menu "Code maturity level options"

Remove the top level menu "Code maturity level options", and moves its
options into menu "General setup".

This makes Kconfig less cluttered and easier to setup.

Signed-off-by: Al Boldi <a1426z@gawab.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>