Update or Remove link to Troubleshooting XPI about sumo

[philipp-sumo]

the way to extract about:support data with the help of this addon during the aaq flow was used before a dedicated api for this got introduced in firefox 36 and probably only shown for users of very outdated browser versions: https://bugzilla.mozilla.org/show_bug.cgi?id=1079563

this was way before the webextension days and the referenced addon is probably no longer hosted on AMO - we should just remove it from the aaq flow.

[jscher2000]

This is still a frequent problem:

• https://support.mozilla.org/questions/1280647
• https://support.mozilla.org/questions/1280119
• https://support.mozilla.org/questions/1279637
• https://support.mozilla.org/questions/1276405
• https://support.mozilla.org/questions/1275608
• https://support.mozilla.org/questions/1274685
• https://support.mozilla.org/questions/1273602
• https://support.mozilla.org/questions/1271956
• https://support.mozilla.org/questions/1270528
• https://support.mozilla.org/questions/1270113

[akatsoulas]

mozilla/kitsune#4227