fs/netfs: remove unused enum choice NETFS_READ_HOLE_CLEAR

fs/netfs: remove unused enum choice NETFS_READ_HOLE_CLEAR

This choice was added by commit 3a11b3a86366 ("netfs: Pass more
information on how to deal with a hole in the cache") but the last
user was removed by commit 86b374d061ee ("netfs: Remove
fs/netfs/io.c").

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/20250519134813.2975312-6-dhowells@redhat.com
cc: Paulo Alcantara <pc@manguebit.com>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>