remove IOHandler stuff

as all code using IO handlers has been changed to use
secop.rwhandler, IO handlers can be removed

Change-Id: Id57fbc4ce2744dbe73bb8792fd45449373f76bb5
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/28526
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/params.py

@@ -141,9 +141,6 @@ class Parameter(Accessible):
     optional = Property(
         '[internal] is this parameter optional?', BoolType(),
         export=False, settable=False, default=False)
-    handler = Property(
-        '[internal] overload the standard read and write functions', ValueType(),
-        export=False, default=None, settable=False)
     initwrite = Property(
         '''[internal] write this parameter on initialization