servo: Merge #12205 - resource: Remove the duplicated config from pref.json (from saneyuki:prefs-cleanup); r=frewsxcv

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---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [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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Source-Repo: https://github.com/servo/servo
Source-Revision: 9860584edf8e1ae4783d6ac4d75bda6b06da2057

servo/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,

servo/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,