To remove unwanted pages from Google, add a noindex tag to the page header or...

https://wiki-tonic.win/index.php/How_to_Remove_a_Subdomain_From_Google_Search_Results:_A_Technical_Guide

To remove unwanted pages from Google, add a noindex tag to the page header or return a 404/410 status code. These methods tell search engines to drop the content from their index permanently