chore(tvix/store): remove old implementations

These were implementing against the (more complicated) gRPC interface,
for which we now have a wrapper.

Change-Id: I0a8284493718ab99618a1d21a76df4d173edb899
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8100
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

tvix/store/src/tests/mod.rs

@@ -1,3 +1 @@
-mod directory_service;
 mod nar_renderer;
-mod path_info_service;