[libc++][NFC] Remove outdated comment in CI pipeline definition

GitOrigin-RevId: 7d855bb8e133720ac1555dc189d9f41e7a50ea93
diff --git a/utils/ci/buildkite-pipeline.yml b/utils/ci/buildkite-pipeline.yml
index 755f98d..d0be2b9 100644
--- a/utils/ci/buildkite-pipeline.yml
+++ b/utils/ci/buildkite-pipeline.yml
@@ -688,7 +688,7 @@
       agents:
         queue: "libcxx-builders"
         os: "macos"
-        arch: "x86_64" # We need to use x86_64 for back-deployment CI, since the old dylibs were compiled for x86_64
+        arch: "x86_64"
       retry:
         automatic:
           - exit_status: -1  # Agent was lost
@@ -703,7 +703,7 @@
       agents:
         queue: "libcxx-builders"
         os: "macos"
-        arch: "x86_64" # We need to use x86_64 for back-deployment CI, since the old dylibs were compiled for x86_64
+        arch: "x86_64"
       retry:
         automatic:
           - exit_status: -1  # Agent was lost