chore(tvix/castore): remove dependency on anyhow

We don't use this here, except in a test, where we don't really use
it either.

Change-Id: Ia6c45fccf663fe328942b1e1a2cd1c3a1b7f9ae5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9376
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/castore/src/directoryservice/grpc.rs

@@ -355,7 +355,7 @@ mod tests {
     };
 
     #[test]
-    fn test() -> anyhow::Result<()> {
+    fn test() {
         let tmpdir = TempDir::new().unwrap();
         let socket_path = tmpdir.path().join("socket");
 
@@ -535,7 +535,5 @@ mod tests {
                     .expect_err("must fail");
             }
         });
-
-        Ok(())
     }
 }