Remove ignored bot_update "force" parameter.

scripts/slave/recipes/chromium_trybot.expected/runhooks_failure.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 246 matching lines @@
       "--revision_mapping_file",
       "{\"src\": \"got_revision\", \"src/buildtools\": \"got_buildtools_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/angle\": \"got_angle_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--git-cache-dir",
       "[GIT_CACHE]",
       "--rietveld_server",
       "https://codereview.chromium.org",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "src@f27fede2220bcd326aee3e86ddfd4ebd0fe58cb9",
-      "--force",
       "--output_manifest"
     ],
     "cwd": "[BUILDER_CACHE]\\win",
     "env": {
       "PATH": "%(PATH)s;RECIPE_PACKAGE_REPO[depot_tools]"
     },
     "name": "bot_update (without patch)",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
       "@@@STEP_LOG_LINE@json.output@{@@@",
@@ skipping 86 matching lines @@
       "@@@SET_BUILD_PROPERTY@failure_hash@\"c18cfb87382155d691c887ecad8e8bf7cdf0fab3\"@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "Step('gclient runhooks (without patch)') failed with return_code 1",
     "recipe_result": null,
     "status_code": 1
   }
 ]