powerpc/perf/hv-24x7: Drop event_24x7_request()

The function event_24x7_request() is essentially a wrapper to the
function single_24x7_request() and can be dropped to simplify code.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>