[recipes] Remove build environment vars from default_env

infra/bots/recipes/swarm_housekeeper.expected/Housekeeper-PerCommit-Trybot.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",
       "[SLAVE_BUILD]/tmp",
       "511"
     ],
     "name": "makedirs tmp_dir",
@@ skipping 12 matching lines @@
   },
   {
     "cmd": [
       "python",
       "[SLAVE_BUILD]/skia/platform_tools/android/tests/run_all.py"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
     "env": {
       "BUILDTYPE": "Release",
       "CHROME_HEADLESS": "1",
-      "GYP_DEFINES": "skia_shared_lib=1 skia_warnings_as_errors=0",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "android platform self-tests"
   },
   {
     "cmd": [
       "python",
       "RECIPE_MODULE[skia::core]/resources/run_binary_size_analysis.py",
       "--library",
       "[SLAVE_BUILD]/out/Release/lib/libskia.so",
       "--githash",
       "abc123",
       "--gsutil_path",
       "[DEPOT_TOOLS]/third_party/gsutil/gsutil",
       "--issue_number",
       "500"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
     "env": {
       "BUILDTYPE": "Release",
       "CHROME_HEADLESS": "1",
-      "GYP_DEFINES": "skia_shared_lib=1 skia_warnings_as_errors=0",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "generate and upload binary size data"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]