EmacsMirror takes a long time to clone

[raxod502]

One bad piece of UX of straight.el currently is that as soon as you hit either a built-in package or a package on EmacsMirror, then straight.el tries to clone EmacsMirror, and this takes forever—even on a fast network connection. I think we can fix this problem.

The easiest way, IMO, would be to extend gnu-elpa-mirror to maintain a mirror of the epkgs repository with the SQLite database file removed. This would effectively solve the problem because the resulting repository would be tiny and fast to clone.

[tarsius]

Since emacsmirror/epkgs@35d6f35 the epkgs repository no longer tracks a sqlite database. Instead of the binary database file epkgs.sqlite it tracks a text file epkgs.sql, from which the former is created on the client-side.

The epkgs repository does not contain any history from before this change. That history is preserved in a separate repository epkgs-v4.

time git clone git@github.com:emacsmirror/epkgs.git
Cloning into 'epkgs'...
remote: Enumerating objects: 83, done.
remote: Counting objects: 100% (83/83), done.
remote: Compressing objects: 100% (25/25), done.
remote: Total 2876 (delta 61), reused 76 (delta 58), pack-reused 2793
Receiving objects: 100% (2876/2876), 15.90 MiB | 9.17 MiB/s, done.
Resolving deltas: 100% (2192/2192), done.

real    0m14.455s
user    0m35.813s
sys     0m0.387s

[raxod502]

Ah, lovely! We can remove this piece of infrastructure, then: #700