qapi/block-core: Drop drive-backup's "Any other error" documentation

We've always been rather lax about documenting errors.  Many "Errors"
sections are obviously not exhaustive.  Only drive-backup is explicit
about this: "Any other error returns a GenericError".

Not useful.  Drop.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240911132459.2548063-3-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/qapi/block-core.json b/qapi/block-core.json
index d3f076d..5c2b3ac 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1858,7 +1858,6 @@
 #
 # Errors:
 #     - If @device does not exist, DeviceNotFound
-#     - Any other error returns a GenericError.
 #
 # Since: 1.3
 #