Revert "tracing: Introduce pipe_cpumask to avoid race on trace_pipes"

This reverts commit 9ef5c25b which is
commit c2489bb7 upstream.

It breaks the Android kabi and is not needed for Android systems.  If it
is needed in the future, it can be brought back in an abi-safe way.

Bug: 161946584
Change-Id: I014d4486d85641031f816da38b00c593dcb8eae6
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>