Replace all os.remove calls

os.remove raises an exception when deleting read-only files on
Windows. Replace all calls with calls to platform_utils.remove,
which deals with deals with that issue.

Change-Id: I4dc9e0c9a36b4238880520c69f5075eca40f3e66
diff --git a/git_config.py b/git_config.py
index 9d5874a..3ba9dbd 100644
--- a/git_config.py
+++ b/git_config.py
@@ -42,6 +42,7 @@
 
 from signal import SIGTERM
 from error import GitError, UploadError
+import platform_utils
 from trace import Trace
 if is_python3():
   from http.client import HTTPException
@@ -268,7 +269,7 @@
     try:
       if os.path.getmtime(self._json) \
       <= os.path.getmtime(self.file):
-        os.remove(self._json)
+        platform_utils.remove(self._json)
         return None
     except OSError:
       return None
@@ -280,7 +281,7 @@
       finally:
         fd.close()
     except (IOError, ValueError):
-      os.remove(self._json)
+      platform_utils.remove(self._json)
       return None
 
   def _SaveJson(self, cache):
@@ -292,7 +293,7 @@
         fd.close()
     except (IOError, TypeError):
       if os.path.exists(self._json):
-        os.remove(self._json)
+        platform_utils.remove(self._json)
 
   def _ReadGit(self):
     """