afs: remove afs_cache_netfs and afs_zap_permits() declarations

afs_zap_permits() has been removed since
commit be080a6f ("afs: Overhaul permit caching").

afs_cache_netfs has been removed since
commit 523d27cd

 ("afs: Convert afs to use the new fscache API").

so remove the declare for them from header file.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/20220909070353.1160228-1-cuigaosheng1@huawei.com/