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

Author: PeterChou1

llvm/include/llvm/Support/Mustache.h

@@ -220,7 +220,6 @@ add_llvm_component_library(LLVMSupport
   MD5.cpp
   MSP430Attributes.cpp
   MSP430AttributeParser.cpp
-  Mustache.cpp      
   NativeFormatting.cpp
   OptimizedStructLayout.cpp
   Optional.cpp