Don’t show “Edit on GitHub” link on docs generated from modules

[alexwlchan]

Moving from pyca/cryptography#3137 – if you have a docs page generated from a module, it shows an “Edit on GitHub” link that points to a non-existent RST file.

It would be nice to either:

• Point that link at the correct file, or
• Hide the link when it points to a non-existent page

I have a vague memory of doing something similar once before, so I might have a go at this when I’m a bit less busy.

[alexwlchan]

Aha, found it: 6360a2e.

Not quite the same because I was hiding the link on a page which didn’t have a corresponding source file – but as a short-term fix, something like that might be better than leaving broken links around.

[Blendify]

Duplicate of #252