[PATCH remotenames V3] remotenames: remove support for old remotenames file format

[Sean Farley]

Jun Wu <quark at fb.com> writes:

> I love this 100ms speed-up. If we want to support the old format, I think it
> is doable by making "branches" lazy and testing "if rname in bookmarks"
> first. Alternatively, we may want to find a way to disable "branches"
> more completely.
>
> I prefer dropping support. Will let smf decide.

I'm fine with dropping support (this is a very experimental extension).
I'm still processing the journal patch so I'm behind on reviewing this
one.