chore: remove defunct file and todo

dev_extension.bzl was a temporary hack that is no longer necessary.

Along the way, also remove a TODO that is defunct.

PiperOrigin-RevId: 690879423

Author: rickeylev

MODULE.bazel

@@ -10,8 +10,6 @@ bazel_dep(name = "rules_license", version = "0.0.4")
 
 # ===== The rest of these are development dependencies =====
 
-# TODO(https://github.com/bazelbuild/stardoc/issues/117): stardoc doesn't yet
-# work with bzlmod enabled. This defines the repo so load() works.
 bazel_dep(
     name = "stardoc",
     version = "0.7.1",