Don't add default repositories and their dependencies in YMP

[hellcp]

Issue Description

YMP adds a lot of repositories which are already default for the system, and dependencies of those repos, which shouldn't be there to begin with.

Expected Result

YMP doesn't add default distro repositories and their dependencies, so only installs dependencies added on top of the distro repos added in OBS, their dependencies as well as the repo itself.

How to Reproduce

1. Go to https://software.opensuse.org/ymp/games/openSUSE_Tumbleweed/urbanterror.ymp (it's easier to point at the proxy and not the api, not that it matters)
2. See that there are openSUSE:Tumbleweed/standard and openSUSE:Factory/ports repos recommended

Further Information

The situation gets even worse with openSUSE:Leap repos, since recently there are also SLE repos added, which have dependencies in repositories through every SP back to the original SLE GA
https://software.opensuse.org/ymp/games/15.4/urbanterror.ymp