BuddyPress.org

Manually delete the existing entries.
Place this in your theme/functions.php or in bp-custom.php to prevent creation of new entries.

function bp_activity_do_not_save( $activity_object ) {
	$exclude = array(
	        'updated_profile',
	        'new_member'
	    );
	
	if( in_array( $activity_object->type, $exclude ) )
		$activity_object->type = false;
}
add_action('bp_activity_before_save', 'bp_activity_do_not_save', 10, 1 );