Eliminate "Immediate" flag from CompilerInvocation.

This adds some ugliness in the current swift binary because we weren't
bothering to set a requested action before, but it keeps things simpler
elsewhere. (Thanks, Connor.)

Swift SVN r13067

lib/Frontend/CompilerInvocation.cpp

@@ -680,11 +680,6 @@ bool CompilerInvocation::parseArgs(ArrayRef<const char *> Args,
     return true;
   }
 
-  if (FrontendOpts.RequestedAction == FrontendOptions::REPL ||
-      FrontendOpts.RequestedAction == FrontendOptions::Immediate) {
-    setImmediate(true);
-  }
-
   if (ParseLangArgs(LangOpts, *ParsedArgs, Diags)) {
     return true;
   }