Bug 893514 - Remove "en-US" and update links to SUMO in /firefox/update page
1. We shouldn't have en-US hard-coded in links to let the locale redirection work on SUMO
2. Links are out of date, so we end up having 3 redirects and broken anchors even on en-US
Merge branch 'bug893514' of https://github.com/flodolo/bedrock into bug893514