Use newly introduced get_leapp_packages function

Let's refactor the code using the brand new library function
specifically introduced for this exact purpose.

repos/system_upgrade/common/actors/scancustommodifications/libraries/scancustommodifications.py

@@ -2,8 +2,7 @@
 import os
 
 from leapp.exceptions import StopActorExecution
-from leapp.libraries.common import dnfconfig
-from leapp.libraries.common.config.version import get_source_major_version, get_target_major_version
+from leapp.libraries.common import rpms
 from leapp.libraries.stdlib import api, CalledProcessError, run
 from leapp.models import CustomModifications
 
@@ -18,17 +17,11 @@ def _get_dirs_to_check(component):
 
 
 def _get_rpms_to_check(component=None):
-    # NOTE(ivasilev) Still not sure that library function is the way to go as looks like leapp file changes have
-    # to be handled differently, and configuration change has to be tracked only for leapp-repository as well.
-    # Let's keep it here for now but I am probably switching to LEAPP_PKG and LEAPP_REPO_PKG in the next commit.
-    leapp_installation = set(dnfconfig.get_leapp_packages()) - set(LEAPP_PACKAGES_TO_IGNORE)
-    leapp_repo = ['leapp-upgrade-el{source}toel{target}'.format(source=get_source_major_version(),
-                                                                target=get_target_major_version())]
     if component == 'repository':
-        return leapp_repo
+        return rpms.get_leapp_packages(component=rpms.LeappComponents.REPOSITORY)
     if component == 'framework':
-        return list(leapp_installation - set(leapp_repo))
-    return list(leapp_installation)
+        return rpms.get_leapp_packages(component=rpms.LeappComponents.FRAMEWORK)
+    return rpms.get_leapp_packages(components=[rpms.LeappComponents.REPOSITORY, rpms.LeappComponents.FRAMEWORK])
 
 
 def deduce_actor_name(a_file):