Revert "Introduce a TypeSystem interface to support adding non-clang languages."

This seems to break expression evaluation on the linux build.

llvm-svn: 239366
diff --git a/lldb/source/DataFormatters/CXXFormatterFunctions.cpp b/lldb/source/DataFormatters/CXXFormatterFunctions.cpp
index 507d671..49eacee 100644
--- a/lldb/source/DataFormatters/CXXFormatterFunctions.cpp
+++ b/lldb/source/DataFormatters/CXXFormatterFunctions.cpp
@@ -312,8 +312,7 @@
     if (data_addr == 0 || data_addr == LLDB_INVALID_ADDRESS)
         return false;
 
-    ClangASTContext* lldb_ast = valobj.GetClangType().GetTypeSystem()->AsClangASTContext();
-    clang::ASTContext* ast = lldb_ast ? lldb_ast->getASTContext() : nullptr;
+    clang::ASTContext* ast = valobj.GetClangType().GetASTContext();
     
     if (!ast)
         return false;