Revert "Return a named error in the result object of an expression with no result"

This reverts commit r344647.
This causes build failures with [-Werror, -Wswitch]. Some cases where the newly
introduced enum value is not handled in particular are in:
  lldb/source/Expression/REPL.cpp:350
  lldb/source/Interpreter/CommandInterpreter.cpp:1529
(maybe there could be more)

As I don't understand lldb to make sure the likely trivial fixes are
correct and also as they might need additional tests, leaving to the
author to resolve.

llvm-svn: 344722
diff --git a/lldb/source/Expression/ExpressionSourceCode.cpp b/lldb/source/Expression/ExpressionSourceCode.cpp
index 2c8f77b..abbb332 100644
--- a/lldb/source/Expression/ExpressionSourceCode.cpp
+++ b/lldb/source/Expression/ExpressionSourceCode.cpp
@@ -256,7 +256,7 @@
     }
 
     ConstString object_name;
-    if (1 /* Language::LanguageIsCPlusPlus(frame->GetLanguage())*/) {
+    if (Language::LanguageIsCPlusPlus(frame->GetLanguage())) {
       if (target->GetInjectLocalVariables(&exe_ctx)) {
         lldb::VariableListSP var_list_sp =
             frame->GetInScopeVariableList(false, true);