Nmap XML output has deviated from the DTD.

[ekelly-1898]

Describe the bug
Nmap XML output has deviated from the DTD.
Since dc238cf Nmap can sometimes print taskprogress without a remaining or etc attribute.
This deviates from the DTD here which describes these as required fields.

To Reproduce
Run a reasonable large or slow scan that outputs task progress before 1% completion.
Use XML output.

Expected behavior
The XML output should match the DTD.

Version info (please complete the following information):
Seen in 7.92, looks to have been introduced earlier.

Additional context
This breaks our XML parser, we've fixed by making these values optional on our end.
Perhaps the simpler change here is to change the DTD.

[fyodor]

Thanks @ekelly-rapid7 . I'm adding this to the list of issues we hope to resolve for the next release.