Remove ignored bot_update "force" parameter.

scripts/slave/recipes/client.dynamorio.recipe_autogen.expected/win_xp_dr_nightly.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.dynamorio",
       "--builder",
       "win-xp-dr-nightly",
       "--slave",
       "TestSlave",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_deps': {'dynamorio/tools/buildbot': 'https://github.com/DynamoRIO/buildbot.git'}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'dynamorio', 'url': 'https://github.com/DynamoRIO/dynamorio.git'}]",
       "--root",
       "dynamorio",
       "--revision_mapping_file",
       "{}",
       "--git-cache-dir",
       "[GIT_CACHE]",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "dynamorio@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 32 matching lines @@
       "BOTTOOLS": "[SLAVE_BUILD]/dynamorio/tools/buildbot/bot_tools"
     },
     "name": "nightly suite"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]