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..0b664f60ab875d5653de24b0378632f0cbba8ccd 100644
--- a/tools/gn/filesystem_utils.cc
+++ b/tools/gn/filesystem_utils.cc
@@ -553,21 +553,6 @@ void NormalizePath(std::string* path) {
   path->resize(dest_i);
 }
 
-void ConvertPathToSystem(std::string* path) {
-#if defined(OS_WIN)
-  for (size_t i = 0; i < path->size(); i++) {
-    if ((*path)[i] == '/')
-      (*path)[i] = '\\';
-  }
-#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] == '/')