Manual:$wgRedirectSources

Details
If local interwikis are set up which allow redirects, set this regular expression to restrict URLs which will be displayed as 'redirected from' links.

It might look something like this: $wgRedirectSources = '!^https?://[a-z-]+\.wikipedia\.org/!';

Leave as false to avoid displaying any incoming redirect markers. This does not affect intra-wiki redirects, which don't change the URL.