[recipes] Remove build environment vars from default_env

infra/bots/recipes/swarm_perf.expected/Perf-Win-MSVC-GCE-CPU-AVX2-x86_64-Release.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[SLAVE_BUILD]\\skia\\infra\\bots\\assets\\skp\\VERSION",
       "/path/to/tmp/"
     ],
     "name": "Get downloaded SKP VERSION"
@@ skipping 139 matching lines @@
       "cpu_or_gpu_value",
       "AVX2",
       "model",
       "GCE",
       "os",
       "Win"
     ],
     "env": {
       "BUILDTYPE": "Release_x64",
       "CHROME_HEADLESS": "1",
-      "GYP_DEFINES": "qt_sdk=C:/Qt/4.8.5/ skia_arch_type=x86_64 skia_gpu=0 skia_warnings_as_errors=0 skia_win_debuggers_path=c:/DbgHelp",
       "SKIA_OUT": "[SLAVE_BUILD]\\out"
     },
     "name": "nanobench"
   },
   {
     "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_[SWARM_OUT_DIR]]\\perfdata\\Perf-Win-MSVC-GCE-CPU-AVX2-x86_64-Release\\data",
@@ skipping 12 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.makedirs(path, mode)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]