Remove Psalm crash workaround generate.sh

[IanDelMar]

Remove the Psalm crash workaround in

wordpress-stubs/generate.sh

Line 22 in 8ed494f

sed -i -e 's#callable( mixed $input= )#callable(mixed=)#g' source/wordpress/wp-includes/abilities-api/class-wp-ability.php

once vimeo/psalm#11647 has been merged.

From #412