Adds the `excerpt_remove_footnotes` function to trim footnote anchors from post excerpts. Props: ramonopoly, costdev, mukesh27, mcsf, azaozz. Fixes #58805. Built from https://develop.svn.wordpress.org/trunk@56244 git-svn-id: http://core.svn.wordpress.org/trunk@55756 1a063a9b-81f0-0310-95a4-ce76da25c4cd