Revert "sched/psi: use kernfs polling functions for PSI trigger polling"

This reverts commit 92cc0153 which is
commit aff03707 upstream.

It is part of a patch series that breaks the Android API.  If this
series is needed in Android devices in the future, it can come back in
an ABI-safe manner.

Bug: 161946584
Change-Id: I2c941ec44d5261a914d95591b7918e46f7db825a
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>