Enforce can_use_on_swarming_builders on all tests.

testing/buildbot/chromium.linux.json

 {
   "Android Arm64 Builder (dbg)": {
     "additional_compile_targets": [
       "all"
     ]
   },
   "Android Builder": {
     "additional_compile_targets": [
       "cronet_test_instrumentation_apk",
       "system_webview_apk"
@@ skipping 1456 matching lines @@
   },
   "Blimp Linux (dbg)": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "blimp_browsertests"
       },
       {
+        "swarming": {
+          "can_use_on_swarming_builders": false
+        },
         "test": "blimp_unittests"
       }
     ]
   },
   "Cast Linux": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
@@ skipping 1447 matching lines @@
         "override_compile_targets": [
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       }
     ]
   }
 }