io_uring/zcrx: fix pp destruction warnings

In the Linux kernel, the following vulnerability has been resolved:

io_uring/zcrx: fix pp destruction warnings

With multiple page pools and in some other cases we can have allocated niovs on page pool destruction. Remove a misplaced warning checking that all niovs are returned to zcrx on io_pp_zc_destroy(). It was reported before but apparently got lost.