mkrepo: Remove -b/--backup-remote option

I'm not using it anymore, everything is stored under ~/repos/ .

f634896c-2a9d-11e3-95c1-f0def1836eb5
mkrepo: Insert "repos/" in all URLs

This is a change I made some time ago to have all repos in one place.

e66385be-2a9e-11e3-ba32-f0def1836eb5