Bug 1727644 - Remove unused layers.omtp.release-capture-on-main-thread pref. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D123691

modules/libpref/init/StaticPrefList.yaml

@@ -6550,11 +6550,6 @@
   value: -1
   mirror: once
 
-- name: layers.omtp.release-capture-on-main-thread
-  type: RelaxedAtomicBool
-  value: false
-  mirror: always
-
 - name: layers.orientation.sync.timeout
   type: RelaxedAtomicUint32
   value: (uint32_t)0