Remove ignored bot_update "force" parameter.

scripts/slave/recipes/v8/auto_roll_v8_deps.expected/roll.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.v8.fyi",
       "--builder",
       "Auto-roll - v8 deps",
       "--slave",
       "TestSlavename",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'deps_file': '.DEPS.git', 'managed': True, 'name': 'v8', 'url': 'https://chromium.googlesource.com/v8/v8'}, {'custom_deps': {'src/chrome/test/data/pdf_private': None, 'src/native_client': None, 'src/third_party/WebKit': None, 'src/third_party/skia': None, 'src/third_party/webrtc': None, 'src/tools/valgrind': None, 'src/v8': None}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/chromium/src.git'}]\ntarget_os = ['android', 'win']",
       "--root",
       "v8",
       "--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\", \"v8\": \"got_revision\"}",
       "--git-cache-dir",
       "[GIT_CACHE]",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "v8@HEAD",
-      "--force",
       "--no_shallow",
       "--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@{@@@",
@@ skipping 256 matching lines @@
     ],
     "cwd": "[SLAVE_BUILD]/v8",
     "name": "git cl"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]