Remove forced use of pickle protocol version 2 (issue #115)

Both microscope.client and microscope.deviceserver modules set Pyro to
use pickle with its protocol version 2.  This was done in b9e5c1c
to support both Python 2 and 3 (pickle's protocol version 2 is the
highest supported in Python 2).  However, we now require Python>=3.5
which can handle up to protocol version 4.  Higher protocol versions
are desirable because they bring performance improvements with
support for more native data types.

We could set Pyro.config.PICKLE_PROTOCOL_VERSION to version 4.  This
helps users when client and server are in different Python versions.
However, this forces others to use older protocol versions.  Instead,
the onus should be on users that need something different from the
default.  This can be easily done on the device server config file.

Author: carandraug

microscope/clients.py

@@ -28,7 +28,6 @@
 # Pyro configuration. Use pickle because it can serialize numpy ndarrays.
 Pyro4.config.SERIALIZERS_ACCEPTED.add('pickle')
 Pyro4.config.SERIALIZER = 'pickle'
-Pyro4.config.PICKLE_PROTOCOL_VERSION = 2
 
 LISTENERS = {}
 

microscope/deviceserver.py

@@ -45,7 +45,6 @@
 # Pyro configuration. Use pickle because it can serialize numpy ndarrays.
 Pyro4.config.SERIALIZERS_ACCEPTED.add('pickle')
 Pyro4.config.SERIALIZER = 'pickle'
-Pyro4.config.PICKLE_PROTOCOL_VERSION = 2
 
 ## We effectively expose all attributes of the classes since our
 ## devices don't hold any private data.  The private methods are to