[NFC] Drastically Reduce The Scope of the Global Context

Delete all of the formalism and infrastructure around maintaining our own copy of the global context. The final frontier is the Builtins, which need to lookup intrinsics in a given scratch context and convert them into the appropriate Swift annotations and types. As these utilities have wormed their way through the compiler, I have decided to leave this alone for now.

include/swift/SIL/SILModule.h

@@ -233,9 +233,6 @@ private:
   // The list of SILProperties in the module.
   PropertyListType properties;
 
-  /// The remark output stream used to record SIL remarks to a file.
-  std::unique_ptr<llvm::raw_fd_ostream> silRemarkStream;
-
   /// The remark streamer used to serialize SIL remarks to a file.
   std::unique_ptr<swift::SILRemarkStreamer> silRemarkStreamer;
 
@@ -526,9 +523,7 @@ public:
   swift::SILRemarkStreamer *getSILRemarkStreamer() {
     return silRemarkStreamer.get();
   }
-  void setSILRemarkStreamer(
-      std::unique_ptr<llvm::raw_fd_ostream> &&remarkStream,
-      std::unique_ptr<swift::SILRemarkStreamer> &&remarkStreamer);
+  void installSILRemarkStreamer();
 
   // This is currently limited to VarDecl because the visibility of global
   // variables and class properties is straightforward, while the visibility of