Move DWARFImporterDelegate into ClangImporter and remove DWARFImporter.

This refactors DWARFImporter to become a part of ClangImporter, since
it needs access to many of its implementation details anyway. The
DWARFImporterDelegate is just another mechanism for deserializing
Clang ASTs and once we have a Clang AST, the processing is effectively
the same.

include/swift/AST/ClangModuleLoader.h

@@ -71,32 +71,6 @@ public:
   virtual bool
   isInOverlayModuleForImportedModule(const DeclContext *overlayDC,
                                      const DeclContext *importedDC) = 0;
-
-  /// Look for declarations associated with the given name.
-  ///
-  /// \param name The name we're searching for.
-  virtual void lookupValue(DeclName name, VisibleDeclConsumer &consumer) {}
-
-  /// Look up a type declaration by its Clang name.
-  ///
-  /// Note that this method does no filtering. If it finds the type in a loaded
-  /// module, it returns it. This is intended for use in reflection / debugging
-  /// contexts where access is not a problem.
-  virtual void lookupTypeDecl(StringRef clangName, ClangTypeKind kind,
-                              llvm::function_ref<void(TypeDecl *)> receiver) {}
-
-  /// Look up type a declaration synthesized by the Clang importer itself, using
-  /// a "related entity kind" to determine which type it should be. For example,
-  /// this can be used to find the synthesized error struct for an
-  /// NS_ERROR_ENUM.
-  ///
-  /// Note that this method does no filtering. If it finds the type in a loaded
-  /// module, it returns it. This is intended for use in reflection / debugging
-  /// contexts where access is not a problem.
-  virtual void
-  lookupRelatedEntity(StringRef clangName, ClangTypeKind kind,
-                      StringRef relatedEntityKind,
-                      llvm::function_ref<void(TypeDecl *)> receiver) {}
 };
 
 } // namespace swift