I have been using the epiphany browser beta for a while, having installed it using these instructions. Now that the browser is part of the raspbian distribution, should I continue to include collabora in my /etc/apt/sources.list? If not, is it safe to remove this line and expect epiphany to still be installed/updated since it would now be served from a different repository?
... is it safe to remove this line and expect epiphany to still be installed/updated ...
Yes. Since Epiphany has been officially released for the first time, it is now in the official repositories and so any future updates will be served from there.
If you remove the Collabora line it just means that apt-get won't look there for updates; the software will remain installed.
... should I continue to include collabora in my /etc/apt/sources.list?
That's a matter of personal opinion really. I don't know if Collabora will continue to post the development versions of Epiphany to their PPA, and I don't know if they are even going to continue being involved with the project at all. I haven't researched anything about the future development of Epiphany.
Personally, I would leave the line in the file, but comment it out (put a
# before the line.) This way, if you want to download software from Collabora in the future, you can just un-comment and run