Python code modernization, 3/n (#1157)

* Remove __metaclass__ = type.

for i in $(grep -REl '__metaclass__ = type' plugins/ tests/); do
  sed -e '/^__metaclass__ = type/d' -i $i;
done

* Remove super arguments, and stop inheriting from object.

plugins/module_utils/_platform.py

@@ -128,7 +128,7 @@ def _normalize_arch(arch_str, variant_str):
         return arch_str, variant_str
 
 
-class _Platform(object):
+class _Platform:
     def __init__(self, os=None, arch=None, variant=None):
         self.os = os
         self.arch = arch