Revert "Bug 1991688 - Storage-Access-Headers: Enable Nightly-Only r=bvandersloot" for causing wpt failures

This reverts commit 07f704b.

Author: Sandor Molnar

modules/libpref/init/StaticPrefList.yaml

@@ -4804,7 +4804,7 @@
 # Enable Storage-Access-Headers
 - name: dom.storage_access.headers.enabled
   type: bool
-  value: @IS_NIGHTLY_BUILD@
+  value: false
   mirror: always
 
 # Forward-Declared Storage-access API.