Remove non-existend mirror url for rules_rust

PiperOrigin-RevId: 460963981
diff --git a/WORKSPACE b/WORKSPACE
index c4a5ed2..b2c83dc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -8,7 +8,6 @@
     name = "rules_rust",
     sha256 = "edb87c0d2ba70823fe3df7862676d695599314a4634b9758bd55f0e8f19c2751",
     urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/rules_rust/releases/download/0.4.0/rules_rust-v0.4.0.tar.gz",
         "https://github.com/bazelbuild/rules_rust/releases/download/0.4.0/rules_rust-v0.4.0.tar.gz",
     ],
 )