Privacy: Remove user's email address from personal data export filename.

Use `wp_unique_filename()` to avoid potential collisions instead.

Props xkon, garrett-eclipse, donmhico, Ov3rfly, Clorith, allendav.
Fixes #44197.
Built from https://develop.svn.wordpress.org/trunk@47144


git-svn-id: https://core.svn.wordpress.org/trunk@46944 1a063a9b-81f0-0310-95a4-ce76da25c4cd