ibm_storage: Remove unused _get_os_type method

platform.dist() doesn't exist on Python 3.8+, so this
no longer works.  This method is not called by any
other code.

Change-Id: I97b000ad8eb2bf63aaa0bb110be6ca39b8359a94

cinder/volume/drivers/ibm/ibm_storage/proxy.py

@@ -16,7 +16,6 @@
 import functools
 import gettext
 import inspect
-import platform
 
 from oslo_log import log as logging
 from oslo_utils import timeutils
@@ -240,12 +239,6 @@ class IBMStorageProxy(object):
                 'wwpns': wwpns,
                 'chap': chap}
 
-    @_trace_time
-    def _get_os_type(self):
-        """Gets a string representation of the current os"""
-        dist = platform.dist()
-        return "%s-%s-%s" % (dist[0], dist[1], platform.processor())
-
     def _log(self, level, message, **kwargs):
         """Wrapper around the logger"""
         to_log = _(self.prefix + message)  # NOQA