Remove ignored bot_update "force" parameter.

scripts/slave/recipes/chromium.chromedriver.recipe_autogen.expected/Linux32.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "chromium.chromedriver",
       "--builder",
       "Linux32",
       "--slave",
       "TestSlave",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_deps': {'src/chrome/test/chromedriver/third_party/java_tests': 'https://chromium.googlesource.com/chromium/deps/webdriver'}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/chromium/src.git'}, {'custom_deps': {'src/chrome/test/data/firefox2_profile/searchplugins': None, 'src/chrome/test/data/firefox2_searchplugins': None, 'src/chrome/test/data/firefox3_profile/searchplugins': None, 'src/chrome/test/data/firefox3_searchplugins': None, 'src/chrome/test/data/osdd': None, 'src/chrome/test/data/ssl/certs': None, 'src/data/autodiscovery': None, 'src/data/esctf': None, 'src/data/mach_ports': None, 'src/data/memory_test': None, 'src/data/mozilla_js_tests': None, 'src/data/page_cycler': None, 'src/data/selenium_core': None, 'src/tools/grit/grit/test/data': None, 'src/webkit/data/bmp_decoder': None, 'src/webkit/data/ico_decoder': None, 'src/webkit/data/test_shell/plugins': None, 'src/webkit/data/xbm_decoder': None}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'src-internal', 'url': 'svn://svn.chromium.org/chrome-internal/trunk/src-internal'}]",
       "--root",
       "src",
       "--revision_mapping_file",
       "{\"src\": \"got_revision\", \"src/third_party/WebKit\": \"got_webkit_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--git-cache-dir",
       "[GIT_CACHE]",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "src@HEAD",
-      "--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 177 matching lines @@
       "--factory-properties={\"annotated_script\":\"chromedriver_buildbot_run.py\",\"blink_config\":\"chromium\",\"gclient_env\":{\"DEPOT_TOOLS_UPDATE\":\"0\",\"LANDMINES_VERBOSE\":\"1\"},\"needs_webdriver_java_tests\":true,\"use_xvfb_on_linux\":true}"
     ],
     "name": "annotated_steps"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]