Revert "x86: Fix __get_wchan() for !STACKTRACE"

This reverts commit e43191f9 which is
commit 5d1ceb39 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: I00c6b2c5b4ca421c57bbc4b0db2dbe3cde0a06d4
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>