This worked for me.
function remove_width_and_height_attribute( $html ) {
return preg_replace( '/(height|width)="\d*"\s/', "", $html );
}
and then change
wp_get_attachment_image_src( $attachment_id, 'full' );
to
remove_width_and_height_attribute(wp_get_attachment_image_src( $attachment_id, 'full' ));