Move benchmark codes to astropy core lib and only keep results here

[pllim]

As asked by @Cadair , is there any good reason why the benchmarking code cannot be in astropy repo? Can we move the code to astropy and only keep the results here?

@astrofrog , do you remember why this is a separate repo?

[astrofrog]

Historically this was because we kept results and benchmarks in the same branch so it made sense to keep this in a separate repo. But since the results and benchmarks live on a different branch anyway I think the benchmarks could just live in the main repo. Having said that I don't know how asv would deal with the list of benchmarks changing over time. If someone can show it would work, I'd be on board with this!

[Cadair]

asv appears to handle it fine on our initial testing with sunpy

[astrofrog]

I guess one definite limitation is that we wouldn't be able to run benchmarks backwards, on older commits, right?

[Cadair]

You appear to still be able to do that, asv appears to read the benchmarks from the latest commit and then runs them on older code.

[MridulS]

I guess we should probably not be moving the benchmarks to the core lib? astropy/astropy#15779 (comment) It will be a lot of data and other files.