Revert "reapply [llvm] add support for mustache templating language" (#131228)

This broke:

https://lab.llvm.org/buildbot/#/builders/64/builds/2486
https://lab.llvm.org/buildbot/#/builders/146/builds/2476

GitOrigin-RevId: 08d15e3f64e3a5ec0adeae0df7969c81ab61d44b
5 files changed