#!/usr/bin/perl

# http://perlmonks.org/?node_id=1189470

use strict;
use warnings;

$_ = do { local $/; <DATA> };

1 while s/^(\d+\|{3}).*\K\|{3}\n\1/; /m;

print;

__DATA__
21997|||70049,,20170428154818,20170527235959|||
21997|||70070,,20170428154739,20170527235959|||

21998|||70049,,20170428154818,20170527235959|||
21998|||70070,,20170428154739,20170527235959|||
21998|||70071,,20170428154739,20170527235959|||