Remove the silent filesystem we no longer need in the new LLVM branch

Author: hyp

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -169,35 +169,6 @@ static bool isSwiftDependencyKind(ModuleDependencyKind Kind) {
          Kind == ModuleDependencyKind::SwiftPlaceholder;
 }
 
-// Wrap the clang file mapping overlay filesystems in a proxy filesystem,
-// to avoid enumerating the overlay filesystems in a `visitChildFileSystems`,
-// as clang's dependency scanner tries to validate that the number of
-// overlay file systems used is the same as the number of `-ivfsoverlay`
-// flags passed through the clang invocation. This validation causes an
-// assertion failure if the filesystem isn't hidden.
-// We don't need to expose the clang importer overlay filesystem to clang's
-// dependency scanner, as it only needs to optimize overlay VFS that are
-// explicitly passed to it via `-ivfsoverlay`.
-class SilentClangImporterOverlayWrapperFS : public llvm::vfs::ProxyFileSystem {
-public:
-  SilentClangImporterOverlayWrapperFS(
-      llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
-      llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> baseFS)
-      : llvm::vfs::ProxyFileSystem(fs), baseFS(baseFS) {}
-
-  void visitChildFileSystems(VisitCallbackTy Callback) override {
-    // Do not forward to proxy, instead count the base and forward
-    // to base directly, bypassing the installed clang overlay filesystems.
-    if (baseFS) {
-      Callback(*baseFS);
-      baseFS->visitChildFileSystems(Callback);
-    }
-  }
-
-private:
-  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> baseFS;
-};
-
 static llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
 getClangInvocationOverlayScanningVFS(
     ASTContext &ctx, llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> baseFS) {