Tools: Include mediawiki::multimedia::fonts in exec_environ

When I previously included mediawiki::multimedia::fonts in
role::labs::tools::execnode to resolve bug #58740 in change
I421685039b7ae9f73535ac92b3d8b6e5ecf1b1ac, I did so under the
apparently wrong impression that only roles should include classes.
The net effect however was that the fonts were only installed on
"true" execution nodes and not on the bastion or webserver nodes,
making for a rather strange setup.

At user request and with more logic, this change moves the include to
toollabs::exec_environ so that the fonts are installed on all nodes
where they are actually expected and needed.

Bug: 66354
Change-Id: Ie071002eef9d4824d7b70de0c6bdeb679450cca4