don't require all versions to be defined for obsoleted keys

in releases where we do not have any obsoleted keys, we still had to
define an entry (with an empty list), as otherwise the code would fail

instead, we can catch the KeyError and carry on as nothing happened

repos/system_upgrade/common/actors/removeobsoletegpgkeys/libraries/removeobsoleterpmgpgkeys.py

@@ -12,11 +12,14 @@ def _get_obsolete_keys():
     distribution = api.current_actor().configuration.os_release.release_id
     obsoleted_keys_map = get_distribution_data(distribution).get('obsoleted-keys', {})
     keys = []
-    for version in range(7, int(get_target_major_version()) + 1):
-        for key in obsoleted_keys_map[str(version)]:
-            name, version, release = key.rsplit("-", 2)
-            if has_package(InstalledRPM, name, version=version, release=release):
-                keys.append(key)
+    try:
+        for version in range(7, int(get_target_major_version()) + 1):
+            for key in obsoleted_keys_map[str(version)]:
+                name, version, release = key.rsplit("-", 2)
+                if has_package(InstalledRPM, name, version=version, release=release):
+                    keys.append(key)
+    except KeyError:
+        pass
 
     return keys