[rpmbuild] drop SCM parameters from copr-rpmbuild
    
    - It allowed building packages without needing a task definition.
      This sounds positive, but as a consequence, the task definition
      needed to be artificially constructed inside the copr-rpmbuild
    
    - It was not used within Copr infrastructure and therefore violated
      the main purpose of copr-rpmbuild, which is reproducing Copr build
      the same way it was done in Copr
    
    - To some extent, it just duplicated what rpkg does