GN: Move towards only using / on Windows

tools/gn/escape.h

Index: tools/gn/escape.h
diff --git a/tools/gn/escape.h b/tools/gn/escape.h
index 1e4fa6897719cd8148e2fc84fdd773bd2898f259..ad28227424a30e0523d3529f3dd1a00abc524848 100644
--- a/tools/gn/escape.h
+++ b/tools/gn/escape.h
@@ -28,15 +28,11 @@ enum EscapingMode {
 struct EscapeOptions {
   EscapeOptions()
       : mode(ESCAPE_NONE),
-        convert_slashes(false),
         inhibit_quoting(false) {
   }
 
   EscapingMode mode;
 
-  // When set, converts forward-slashes to system-specific path separators.
-  bool convert_slashes;
-
   // When the escaping mode is ESCAPE_SHELL, the escaper will normally put
   // quotes around things with spaces. If this value is set to true, we'll
   // disable the quoting feature and just add the spaces.