Combine “Exclude” Query in functions.php

Just put both if statements with || (or) in the one callback function:

function wpse_283481_exclude_posts( $query ) {
    if ( ( $query->is_main_query() && $query->is_home() ) || $query->is_feed() ) { 
        $query->set( 'cat', '-103' ); 
    }
}
add_action( 'pre_get_posts', 'wpse_283481_exclude_posts' );