[clangd] No need to setTraversalScope in SemanticHighlighting.

[hokein]

Summary

We have already set it when the AST is being built, and setting TraversalScope
is not free (it will clear the cache, which is expensive to build).

[jvikstrom]

lgtm

clang-tools-extra/clangd/SemanticHighlighting.h

 //==-- SemanticHighlighting.h - Generating highlights from the AST-- C++ -*-==//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_SEMANTICHIGHLIGHT_H
-#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SEMANTICHIGHLIGHT_H
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_SEMANTICHIGHLIGHTING_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_SEMANTICHIGHLIGHTING_H
 
 #include "ClangdUnit.h"
 
 namespace clang {
 namespace clangd {
 
 enum class HighlightingKind {
   Variable,

clang-tools-extra/clangd/SemanticHighlighting.cpp

-//===--- SemanticHighlighting.cpp - -------------------------- ---*- C++ -*-===//
+//===--- SemanticHighlighting.cpp - ------------------------- ---*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "SemanticHighlighting.h"

 
 } // namespace
 
 bool operator==(const HighlightingToken &Lhs, const HighlightingToken &Rhs) {
   return Lhs.Kind == Rhs.Kind && Lhs.R == Rhs.R;
 }
 
 std::vector<HighlightingToken> getSemanticHighlightings(ParsedAST &AST) {
-  AST.getASTContext().setTraversalScope(AST.getLocalTopLevelDecls());
   return HighlightingTokenCollector(AST).collectTokens();
 }
 
 } // namespace clangd
 } // namespace clang