lockdep/selftests: Use SBRM APIs for wait context tests

The "__cleanup__" attribute is already used for wait context tests, so
using it for locking tests has already been proven working. Now since
SBRM APIs are merged, let's use these APIs instead of a local guard
framework. This also helps testing SBRM APIs.

Note that originally the tests don't rely on the cleanup ordering of
two variables in the same scope, but since now it's something we'd like
to assume and rely on[1], drop the extra scope in inner_in_outer()
function. Again this gives us another opportunity to test the compiler
behavior.

[1]: https://lore.kernel.org/lkml/CAHk-=whEsr6fuVSdsoNPokLR2fZiGuo_hCLyrS-LCw7hT_N7cQ@mail.gmail.com/
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230715235257.110325-1-boqun.feng@gmail.com