ansible: remove seemingly unused raw_params

Traced git log all the way back to beginning of time, and checked
Ansible versions starting Jan 2016. Zero clue where this came from, but
the convention suggests it came from Ansible at some point.

ansible_mitogen/runner.py

@@ -93,16 +93,13 @@ class Runner(object):
     Subclasses may override `_run`()` and extend `setup()` and `revert()`.
     """
     def __init__(self, module, service_context, emulate_tty=None,
-                 raw_params=None, args=None, env=None):
+                 args=None, env=None):
         if args is None:
             args = {}
-        if raw_params is not None:
-            args['_raw_params'] = raw_params
 
         self.module = utf8(module)
         self.service_context = service_context
         self.emulate_tty = emulate_tty
-        self.raw_params = raw_params
         self.args = args
         self.env = env