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/manifest_xml.py b/manifest_xml.py
index 05651c6..9b5d784 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -166,7 +166,7 @@
 
     try:
       if os.path.lexists(self.manifestFile):
-        os.remove(self.manifestFile)
+        platform_utils.remove(self.manifestFile)
       platform_utils.symlink(os.path.join('manifests', name), self.manifestFile)
     except OSError as e:
       raise ManifestParseError('cannot link manifest %s: %s' % (name, str(e)))