Remove ignored bot_update "force" parameter.

scripts/slave/recipes/client.nacl.sdk.recipe_autogen.expected/mac_sdk_multirel.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.nacl.sdk",
       "--builder",
       "mac-sdk-multirel",
       "--slave",
       "TestSlave",
       "--spec",
       "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_deps': {'src-pdf': None, 'src/pdf': None}, 'custom_vars': {'googlecode_url': 'svn://svn.chromium.org/%s', 'sourceforge_url': 'svn://svn.chromium.org/%(repo)s', 'svn_url': 'svn://svn.chromium.org', 'webkit_trunk': 'svn://svn.chromium.org/blink/trunk'}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'chrome-official', 'url': 'svn://svn.chromium.org/chrome-internal/trunk/tools/buildspec/build/chrome-official'}]",
       "--root",
       "chrome-official",
       "--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",
       "chrome-official@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 113 matching lines @@
       "--factory-properties={\"annotated_script\":\"nacl_sdk_buildbot_run.py\",\"blink_config\":\"chromium\",\"gclient_env\":{\"CHROMIUM_GYP_SYNTAX_CHECK\":\"1\",\"DEPOT_TOOLS_UPDATE\":\"0\",\"GYP_DEFINES\":\"fastbuild=1 component=static_library\",\"GYP_GENERATORS\":\"ninja\",\"LANDMINES_VERBOSE\":\"1\"},\"no_gclient_branch\":true,\"nuke_and_pave\":true}"
     ],
     "name": "annotated_steps"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]