disk_cache_block_remote: always pretend the cache has space
disk_cache_block_remote: always pretend the cache has space

If kbfsgit tried to do a prefetch, it would crash here due to the
recent changes to control prefetches to the working set cache.  For
now, just make it always look like there's space, since those kinds of
fetches won't be coming over the remote protocol.

Issue: keybase/client#15162

keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client