Auto merge of #12205 - saneyuki:prefs-cleanup, r=frewsxcv

resource: Remove the duplicated config from pref.json

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes do not require tests because
  - just clean up.

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resources/package-prefs.json

@@ -23,7 +23,6 @@
   "js.throw_on_debuggee_would_run.enabled": false,
   "js.dump_stack_on_debuggee_would_run.enabled": false,
   "js.werror.enabled": false,
-  "js.strict.enabled": false,
   "js.shared_memory.enabled": true,
   "js.mem.high_water_mark": 128,
   "js.mem.max": -1,

resources/prefs.json

@@ -23,7 +23,6 @@
   "js.throw_on_debuggee_would_run.enabled": false,
   "js.dump_stack_on_debuggee_would_run.enabled": false,
   "js.werror.enabled": false,
-  "js.strict.enabled": false,
   "js.shared_memory.enabled": true,
   "js.mem.high_water_mark": 128,
   "js.mem.max": -1,