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

This reverts commit 10f358cd which is
commit c2489bb7 upstream.

It breaks the Android ABI and is not needed for Android systems at this
point in time.  If needed in the future, it can come back in an abi-safe
way.

Bug: 161946584
Change-Id: I821cce9935fbf264a40b9c089e5591efdf145bcf
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>