Enable PENDING_REF_PREFIX in codereview.settings.

Remove the FORCE_HTTPS_COMMIT_URL as well, since it's no
longer needed after switching to Git.

BUG=chromium:412012
R=agable@chromium.org

Review URL: https://webrtc-codereview.appspot.com/25339004

Cr-Commit-Position: refs/heads/master@{#8846}
diff --git a/codereview.settings b/codereview.settings
index efd13e6..c553b48 100644
--- a/codereview.settings
+++ b/codereview.settings
@@ -7,4 +7,4 @@
 TRYSERVER_PROJECT: webrtc
 TRYSERVER_ROOT: src
 PROJECT: webrtc
-FORCE_HTTPS_COMMIT_URL: True
+PENDING_REF_PREFIX: refs/pending/