[clang-format] Fix a clang-tidy warning, NFC

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306409 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/NamespaceEndCommentsFixer.cpp

@@ -174,7 +174,7 @@ tooling::Replacements NamespaceEndCommentsFixer::analyze(
         AllNamespaceNames = "::" + NamespaceName + AllNamespaceNames;
         continue;
       }
-      NamespaceName += std::move(AllNamespaceNames);
+      NamespaceName += AllNamespaceNames;
       CompactedNamespacesCount = 0;
       AllNamespaceNames = std::string();
     }