Revert "perf/core: Fix endless multiplex timer"

This reverts commit 2cdbfd65 ("perf/core: Fix endless multiplex
timer") as it is not needed because we reverted 0b4c9255
("perf/cgroups: Don't rotate events for cgroups unnecessarily") earlier
as it broke the ABI.

This also fixes the build breakage caused by the above commit being in
the tree and us reverting the original change.

Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I640225fb5db8f81fdf2011cabeb593c6d9f066b7