graphics/lua-gd: the port had been updated and improved (+)

• Update the version 2.0.33r3 (it's not tagged yet, but that's what written inside their Makefile) and unrestrict from the particular version of Lua (now we need to set PKGNAMEPREFIX)
• Simplify building: drop hand-rolled `do-build' target plus associated bits and use upstream routine, slightly adjusted
• Development now happens at GitHub, update MASTER_SITES and the WWW line in the port description accordingly
• Convert to option helpers and optimize some target recipes

PR: 253811