Do not check deleted files with `make fastlint`
    
    when any file from FreeIPA tree has been deleted there was
    a failure like:
     pylint
     ------
     ************* Module ipaserver/install/ntpinstance.py
     ipaserver/install/ntpinstance.py:1: [F0001(fatal), ] No module named ipaserver/install/ntpinstance.py)
    Adding --diff-filter to fastlint will not list deleted files
    in git diff --names-only output to not include not existing
    files to checklist.
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Michal Reznik <mreznik@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>