Stop to use contextmanager for goma.build_with_goma

scripts/slave/recipe_modules/goma/example.expected/linux.json

 [
   {
     "cmd": [],
     "name": "ensure_goma"
   },
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::cipd]/resources/bootstrap.py",
@@ skipping 134 matching lines @@
   {
     "cmd": [
       "echo",
       "50"
     ],
     "name": "echo goma jobs second"
   },
   {
     "cmd": [
       "ninja",
+      "-j",
+      "50",
       "-C",
-      "out/Release",
-      "-j",
-      "500"
+      "out/Release"
     ],
     "name": "ninja"
   },
   {
     "cmd": [],
     "name": "postprocess_for_goma"
   },
   {
     "cmd": [
       "python",
@@ skipping 52 matching lines @@
       "-u",
       "RECIPE_PACKAGE_REPO[build]/scripts/slave/upload_goma_logs.py",
       "--upload-compiler-proxy-info",
       "--json-status",
       "[CACHE]/cipd/goma/jsonstatus",
       "--ninja-log-outdir",
       "out/Release",
       "--ninja-log-compiler",
       "goma",
       "--ninja-log-command",
-      "['ninja', '-C', 'out/Release', '-j', '500']",
+      "['ninja', '-j', 50, '-C', 'out/Release']",
       "--ninja-log-exit-status",
       "0",
       "--goma-stats-file",
       "build_data_dir/goma_stats_proto",
       "--goma-crash-report-id-file",
       "build_data_dir/crash_report_id_file",
       "--build-data-dir",
       "build_data_dir",
       "--buildbot-buildername",
       "test_builder",
@@ skipping 27 matching lines @@
     "~followup_annotations": [
       "@@@STEP_NEST_LEVEL@1@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]