Don't remove surveyChecks unless addon is uninstalled
Don't remove surveyChecks unless addon is uninstalled

- refs #1006
- only call `survey.destroy()` if the addon is being `uninstalled`
we have been calling on `unload`.

ckprice/testpilot,6a68/idea-town,mozilla/testpilot,mozilla/idea-town,fzzzy/testpilot,mathjazz/testpilot,mozilla/idea-town-server,flodolo/testpilot,6a68/testpilot,lmorchard/idea-town,mozilla/idea-town-server,6a68/testpilot,6a68/idea-town,mathjazz/testpilot,mozilla/idea-town-server,meandavejustice/testpilot,flodolo/testpilot,flodolo/testpilot,lmorchard/idea-town,mozilla/testpilot,mathjazz/testpilot,fzzzy/testpilot,lmorchard/testpilot,lmorchard/testpilot,chuckharmston/testpilot,6a68/testpilot,lmorchard/testpilot,chuckharmston/testpilot,lmorchard/idea-town-server,dannycoates/testpilot,6a68/idea-town,mozilla/idea-town,meandavejustice/testpilot,mathjazz/testpilot,clouserw/testpilot,lmorchard/idea-town-server,lmorchard/idea-town,ckprice/testpilot,lmorchard/testpilot,meandavejustice/testpilot,fzzzy/testpilot,6a68/testpilot,ckprice/testpilot,flodolo/testpilot,dannycoates/testpilot,mozilla/idea-town,dannycoates/testpilot,mozilla/idea-town,clouserw/testpilot,mozilla/idea-town-server,ckprice/testpilot,dannycoates/testpilot,lmorchard/idea-town,lmorchard/idea-town-server,mozilla/testpilot,lmorchard/idea-town-server,clouserw/testpilot,6a68/idea-town,fzzzy/testpilot,meandavejustice/testpilot,clouserw/testpilot,chuckharmston/testpilot,mozilla/testpilot,chuckharmston/testpilot