Remove safe browsing support
This is unfortunate, but this feature has been disabled everywhere except Epiphany Tech Preview due to changes in Google's terms of service. We have to keep Google API keys secret now, and it's just not possible unless build secrets are allowed. We can do that in Tech Preview, but Linux distros cannot do this. Keeping the feature around only for ourselves and not for normal users is just not very useful.
Closes #1393 (closed) Closes #1334 (closed) Closes #1699 (closed) Closes #1721 (closed) Related: #682 (closed)