fix doc-comment pointers broken by the module-eval split

Both referenced the now-deleted nix/module-eval.nix. The nix side of
each pairing is spread across multiple files post-split, so drop the
cross-reference rather than chase it across files.

swarm-secret-client/src/path.rs

@@ -166,8 +166,7 @@ mod tests {
         // Renaming any of these is a silent 403 at provision time, not a
         // compile error: the controller's grant spells the mount and root out
         // in `nix/host-modules/swarm-bao.nix` (`controllerPolicyText`), which
-        // no Rust change can reach. Editing here means editing there, and
-        // `nix/module-eval.nix` asserts the other side.
+        // no Rust change can reach. Editing here means editing there.
         assert_eq!(MOUNT, "secret");
         assert_eq!(ROOT, "swarm");