Remove unused function register_column_headers

[michalzuber]

Function that is not used with no return statement.

function register_column_headers($screen, $columns) {
       $wp_list_table = new _WP_List_Table_Compat($screen, $columns);
}

[ocean90]

Maybe not used by core, but what about plugins? Take a look at what _WP_List_Table_Compat does, there is no need to return something.

[michalzuber]

Thank you ocean90, great point, I learned something. PHPDoc over that class says it's for backward compatibilty.