Remove unnecessary demangling operation (hopefully NFC)

[aprantl]

Summary

This extra call to the demangler doesn't affect the performance of C++ because the result is being cached anyway; but I'm working on a patch to the Swift branch that uses extra contextual information to provide a more accurate demangling result. In that case this call would be extra and unnecessary work.

lldb/source/Core/Mangled.cpp

 // Itanium scheme, and defined in a compilation unit within the same module as
 // other C++ units.  In addition, different targets could have different ways
 // of mangling names from a given language, likewise the compilation units
 // within those targets.
 //----------------------------------------------------------------------
 lldb::LanguageType Mangled::GuessLanguage() const {
   ConstString mangled = GetMangledName();
   if (mangled) {
-    if (GetDemangledName(lldb::eLanguageTypeUnknown)) {
-      const char *mangled_name = mangled.GetCString();
-      if (CPlusPlusLanguage::IsCPPMangledName(mangled_name))
-        return lldb::eLanguageTypeC_plus_plus;
-      else if (ObjCLanguage::IsPossibleObjCMethodName(mangled_name))
-        return lldb::eLanguageTypeObjC;
-    }
   } else {
     // ObjC names aren't really mangled, so they won't necessarily be in the
     // mangled name slot.
     ConstString demangled_name = GetDemangledName(lldb::eLanguageTypeUnknown);
     if (demangled_name 
         && ObjCLanguage::IsPossibleObjCMethodName(demangled_name.GetCString()))
       return lldb::eLanguageTypeObjC;