further fixes of py3 issues

complaints by pylint are mainly related to
- remove object from base list in class definitions
- unnecessary else/elif after return/raise

Change-Id: I13d15449149cc8bba0562338d0c9c42e97163bdf
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/21325
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop_ess/epics.py

@@ -27,7 +27,7 @@ from secop.modules import Drivable, Parameter, Readable
 try:
     from pvaccess import Channel  # import EPIVSv4 functionallity, PV access
 except ImportError:
-    class Channel(object):
+    class Channel:
 
         def __init__(self, pv_name):
             self.pv_name = pv_name
@@ -48,7 +48,7 @@ except ImportError:
 try:
     from epics import PV
 except ImportError:
-    class PV(object):
+    class PV:
 
         def __init__(self, pv_name):
             self.pv_name = pv_name