or you can keep in bp-custom.php, if you hook it to init action.
add_action("init","remove_autop_filters_from_activity");
function remove_autop_filters_from_activity(){
remove_filter( 'bp_get_activity_content_body', 'wpautop' );
remove_filter( 'bp_get_activity_content', 'wpautop' );
}
Actually, the remove filter should be called after the filter is actually added.
