i18n: Remove the `script_loader_src` filter from `load_script_textdomain()`.

This filter is superfluous here, the `load_script_textdomain_relative_path` should be used for customising the textdomain path.

Props dimadin.
Merges [44288] to trunk.
See #45528.
Built from https://develop.svn.wordpress.org/trunk@44318


git-svn-id: https://core.svn.wordpress.org/trunk@44148 1a063a9b-81f0-0310-95a4-ce76da25c4cd