Revert "xfrm: Export symbol xfrm_dev_state_delete."

This reverts commit 878c90b5 which is
commit 2d531775 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: I23d442e23701c72125f3d7a1ee42fb6eb0702824
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>