#!/usr/bin/env perl

use strict;
use warnings;

my $re = qr{
    <div \s+ class="sectionHeading">.*?</div>\s+
    <div \s+ class="sectionContent">.*?</div>\s+
}msx;

my $html = do { local $/; <DATA> };

$html =~ s/$re//;

print $html;

__DATA__
<!-- KEEP -->
<div class="sectionHeading">REMOVE_THIS</div>
<div class="sectionContent">
<table class="sectionTable" ...
...
</table>
</div>
<!-- KEEP -->