Fix validation error in explicit-failures-markup.xml

[danieljames]

Fix this validation error:

$ xmllint --schema ~/boost/develop/status/explicit-failures.xsd explicit-failures-markup.xml
explicit-failures-markup.xml:8: parser error : XML declaration allowed only at the start of the document
<?xml version="1.0" encoding="utf-8"?>
`     ^

[lcaminiti]

I fixed by removing the copyright comment from this file. This file will be merged into the main explicit failure markup file and if I put the copyright comment here, it will be repeated in the main file. That done for each lib, will clutter the main file with many copyright comments.

[danieljames]

It won't, the script extracts the 'library' tags and their contents, so it ignores the copyright comment. If you look at the develop branch for unordered, functional, container_hash and quickbook they all have a copyright comment but none of them are copied into the main file.

[lcaminiti]

I see. I added the copyright and licence comment to the file as suggested by this pull request.