FileSystemForLocal was listening on the node's Tailscale address,
which potentially exposes the user's view of TailFS shares to other
Tailnet users. Remote nodes should connect to exported shares via
the peerapi.
This removes that code so that FileSystemForLocal is only avaialable
on 100.100.100.100:8080.
Updates tailscale/corp#16827
Signed-off-by: Percy Wegmann <percy@tailscale.com>