[NFC][Interpreter] Remove unused CompilerInvocation

clang/lib/Interpreter/Interpreter.cpp

if (!llvm::is_contained(ClangArgv, " -x")) {
     ClangArgv.push_back("-x");
     ClangArgv.push_back("c++");
   }
 
   // Put a dummy C++ file on to ensure there's at least one compile job for the
   // driver to construct.
   ClangArgv.push_back("<<< inputs >>>");
 
-  CompilerInvocation Invocation;
   // Buffer diagnostics from argument parsing so that we can output them using a
   // well formed diagnostic object.
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
   IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts =
       CreateAndPopulateDiagOpts(ClangArgv);
   TextDiagnosticBuffer *DiagsBuffer = new TextDiagnosticBuffer;
   DiagnosticsEngine Diags(DiagID, &*DiagOpts, DiagsBuffer);