When `noopener noreferrer` was originally added in #37941 and related tickets, the `noreferrer` bit was specifically included due to Firefox not supporting `noopener` at the time.
Since `noopener` has been supported by all major browsers for a while, it should now be safe to remove the `noreferrer` attribute from core.
Props Mista-Flo, audrasjb, joostdevalk, jonoaldersonwp, peterwilsoncc, elgameel.
Fixes#49558.
git-svn-id: https://develop.svn.wordpress.org/trunk@49215 602fd350-edb4-49c9-b593-d223f7449a82
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