Revert "net: rtnetlink: add helper to extract msg type's kind"

This reverts commit 85c15422 which is
commit 2e9ea3e3 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I8cde97f239eaf15d952948581987bfa4f1bcb28b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>