Update a comment to reflect the middleman-less reality.

And also allay my fears about Bazel being incorrect; I didn't realize it worked this way.

RELNOTES: None.
PiperOrigin-RevId: 695682365
Change-Id: I30305a86a6cc00f3118755d3aff491b1291e9cb3

Author: lberki

src/main/java/com/google/devtools/build/lib/actions/RunfilesArtifactValue.java

@@ -125,20 +125,11 @@ public void forEachTree(RunfilesConsumer<TreeArtifactValue> consumer)
   @Override
   public boolean equals(Object o) {
     // This method, seemingly erroneously, does not check whether the runfilesTree of the two
-    // objects is equivalent. This is because it's costly (it involves flattening nested sets and
-    // even if one caches a fingerprint, it's still a fair amount of CPU) and because it's
-    // currently not necessary: RunfilesArtifactValue is only ever created as the SkyValue of
-    // runfiles tree and those are special-cased in ActionCacheChecker (see
-    // ActionCacheChecker.checkMiddlemanAction()): the checksum of a runfiles tree artifact is the
-    // function of the checksum of all the artifacts on the inputs of the middleman action, which
-    // includes both the artifacts the runfiles tree links to and the runfiles input manifest,
-    // which in turn encodes the structure of the runfiles tree. The checksum of the runfiles tree
-    // artifact is here as the "metadata" field, which *is* compared here, so the
-    // RunfilesArtifactValues of two runfiles middlemen will be equals iff they represent the same
-    // runfiles tree.
-    //
-    // TODO(b/304440811): The above is either not true or true for a different reason.
-    // Check and update the code accordingly.
+    // objects are equivalent. This is because it's unnecessary because the layout of the runfiles
+    // tree is already factored into the equality decision in two ways:
+    // - Through "metadata", which takes the layout into account (see computeDigest())
+    // - Through the runfiles input manifest file, which is part of the runfiles tree, which
+    //   contains the exact mapping and whose digest is in "fileValues"
     if (this == o) {
       return true;
     }