Remove bogus master/builder/slave/force parameters from bot_update.

recipe_modules/bot_update/__init__.py

 DEPS = [
   'gclient',
   'recipe_engine/json',
   'recipe_engine/path',
   'recipe_engine/platform',
   'recipe_engine/properties',
   'recipe_engine/python',
   'recipe_engine/raw_io',
   'rietveld',
   'recipe_engine/step',
   'tryserver',
 ]
 
 from recipe_engine.recipe_api import Property
 from recipe_engine.types import freeze
 
 PROPERTIES = {
-  'mastername': Property(default=None),
-  'buildername': Property(default=None),
-  'slavename': Property(default=None),
   'issue': Property(default=None),
   'patchset': Property(default=None),
   'patch_project': Property(default=None),
   'repository': Property(default=None),
   'event.patchSet.ref': Property(default=None, param_name="gerrit_ref"),
   'rietveld': Property(default=None),
   'revision': Property(default=None),
   'parent_got_revision': Property(default=None),
   'deps_revision_overrides': Property(default=freeze({})),
   'fail_patch': Property(default=None, kind=str),
 }