Remove always-failing MJX build

Author: olupton

.github/container/Dockerfile.mjx

@@ -86,21 +86,6 @@ haliax:
   tracking_ref: main
   latest_verified_commit: 2a696a0c971901ff93afdaa965959d8e3b982ba9
   mode: git-clone
-mujoco:
-  url: https://github.com/google-deepmind/mujoco.git
-  tracking_ref: main
-  latest_verified_commit: e95159b4f6d48d114b16a8dc13ad26b3e44bc3e2
-  mode: git-clone
-mujoco-mpc:
-  url: https://github.com/google-deepmind/mujoco_mpc.git
-  tracking_ref: main
-  latest_verified_commit: 4700f4a13be18398f5aaf6a33ed42e531967e3ae
-  mode: git-clone
-language-to-reward-2023:
-  url: https://github.com/google-deepmind/language_to_reward_2023.git
-  tracking_ref: main
-  latest_verified_commit: abb8e5125e4ecd0da378490b73448c05a694def5
-  mode: git-clone
 mlperf-logging:
   url: https://github.com/mlcommons/logging.git
   tracking_ref: master