[UPDATE] games/linux-q3ademo: clean-up, minor fixes, rename to "linux-quake3-demo"

hanges:

• Clean-up.
• Rename to "linux-quake3-demo" (also rename port directory).
• Add SIZE entry to distinfo.
• Fix symlink with different OpenGL implementations (ports).
• Take maintainership.
• Use SUB_FILES for script.
• Distfile is fetched automatically from MASTER_SITE_GENTOO.

PR: ports/86227
Submitted by: Alejandro Pulver <alejandro@varnet.biz>