pages: remove GNOME Online Accounts from initial setup
The webview was removed from GOA, as it is discouraged by OAuth 2.0 providers like Google. Doing OAuth 2.0 becomes difficult while locking down the host browser and makes less sense as a setup-user only option.
Remove the support from GNOME Initial Setup, with the intention of having GNOME Tour or somewhere else appropriate absorbing it.
closes #202 (closed)