Clean up target_os=llvm now that it does nothing.

infra/bots/recipes/swarm_ct_skps.expected/CT_DM_1m_SKPs_slave3_failure.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[CUSTOM_/_B_WORK]",
       "511"
     ],
     "name": "makedirs checkout_path",
@@ skipping 10 matching lines @@
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[depot_tools]/gclient.py",
       "config",
       "--spec",
-      "cache_dir = '[CUSTOM_/_B_CACHE]'\nsolutions = [{'deps_file': 'DEPS', 'managed': False, 'name': 'skia', 'url': 'https://skia.googlesource.com/skia.git'}]\ntarget_os = ['llvm']"
+      "cache_dir = '[CUSTOM_/_B_CACHE]'\nsolutions = [{'deps_file': 'DEPS', 'managed': False, 'name': 'skia', 'url': 'https://skia.googlesource.com/skia.git'}]"
     ],
     "cwd": "[CUSTOM_/_B_WORK]",
     "env": {
       "BUILDTYPE": "Debug",
       "CHROME_HEADLESS": "1",
       "PATH": "%(PATH)s:RECIPE_PACKAGE_REPO[depot_tools]",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "gclient setup"
   },
@@ skipping 1504 matching lines @@
       "@@@STEP_LINK@view steps on Milo@https://luci-milo.appspot.com/swarming/task/148aa78d7aa0000@@@"
     ]
   },
   {
     "name": "$result",
     "reason": "Failed steps: ct-dm-3 on Ubuntu-14.04",
     "recipe_result": null,
     "status_code": 1
   }
 ]