games/dreamchess: Fix licenses, adopt again

• Fix LICENSE_DISTFILES for all licenses: those set to ${DISTNAME} where set to inexistent distfiles, while the one set to ${DISTNAME}.tar.gz was the wrong distfile.
• Improve style as suggested by portclippy and portfmt.
• Take maintainership again.

Approved by: gerald (mentor)
Differential Revision: https://reviews.freebsd.org/D35279