Description of problem:
Currently there is no way to schedule removal of an etra package from a system.
You can only schedule a package removal based upon package_id (system.schedulePackageRemove). However, for an extra package you can't have package_id. So we need new API call named scheduleExtraPackageRemove or schedulePackageRemovebyNevra that would accept Nevra parameters instead of package_id.


Steps to Reproduce:
1. call system.comparePackages / system.comparePackageProfile to obtain diff list 
2. call to system.schedulePackageRemovebyNevra

Actual results:
there is no such call


Expected results:
possibility to remove extra packages from a system also via API call