Remove io and profiling from default GAP_PKGS_TO_BUILD, instead let gap-actions/process-coverage take care of them

[fingolfin]

See gap-actions/process-coverage#4

We only need those for processing coverage, so this makes sense, and saves a bit of time for packages don't needing those. It also is conceptually simpler: packages don't need to "remember" to add those to GAP_PKGS_TO_BUILD. Of course packages which currently specify such a GAP_PKGS_TO_BUILD will keep working for now.

(Some care must be taken so that the io and profiling packages themselves keep working, but I think that's not difficult to do, as long as one is aware).