Remove ignored bot_update "force" parameter.

scripts/slave/recipes/client.drmemory.recipe_autogen.expected/win_xp_drm.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]\\resources\\bot_update.py",
       "--master",
       "client.drmemory",
       "--builder",
       "win-xp-drm",
       "--slave",
       "TestSlave",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_deps': {'drmemory/dynamorio': 'https://github.com/DynamoRIO/dynamorio.git', 'tools/buildbot': 'https://github.com/DynamoRIO/buildbot.git'}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'drmemory', 'url': 'https://github.com/DynamoRIO/drmemory.git'}]",
       "--root",
       "drmemory",
       "--revision_mapping_file",
       "{}",
       "--git-cache-dir",
       "[GIT_CACHE]",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "drmemory@123456789abcdef",
-      "--force",
       "--output_manifest"
     ],
     "env": {
       "PATH": "%(PATH)s;RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"did_run\": true, @@@",
@@ skipping 192 matching lines @@
     "~followup_annotations": [
       "@@@STEP_LINK@gsutil.upload@https://storage.cloud.google.com/chromium-drmemory-builds/testlogs/from_win-xp-drm@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]