This is only relevant to non embeddable URLs.
After first init, markers were set but not removed,
causing an edited URL to revert when switching to text mode
or any paragraph after the URL to just contain that URL.
Fixes#33954.
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git-svn-id: http://core.svn.wordpress.org/trunk@35182 1a063a9b-81f0-0310-95a4-ce76da25c4cd