s390/perf: remove perf_release/reserver_sampling functions

Now that the oprofile sampling code is gone there is only one user of
the sampling facility left. Therefore the reserve and release
functions can be removed.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>