GN: Move towards only using / on Windows

tools/gn/filesystem_utils.cc

Index: tools/gn/filesystem_utils.cc
diff --git a/tools/gn/filesystem_utils.cc b/tools/gn/filesystem_utils.cc
index 18d31d0a7ab016d6afcdb7f794ac586581855079..10837621c3e4bb7d45e26c2ac400db1b00ce1adb 100644
--- a/tools/gn/filesystem_utils.cc
+++ b/tools/gn/filesystem_utils.cc
@@ -562,12 +562,6 @@ void ConvertPathToSystem(std::string* path) {
 #endif
 }
 
-std::string PathToSystem(const std::string& path) {
-  std::string ret(path);
-  ConvertPathToSystem(&ret);
-  return ret;
-}
-
 std::string RebaseSourceAbsolutePath(const std::string& input,
                                      const SourceDir& dest_dir) {
   CHECK(input.size() >= 2 && input[0] == '/' && input[1] == '/')