WEB: Update credits to retire BeOS porter Stefan Parviainen

Quoth Luc Schrijvers (Begasus) on scummvm-devel:
"BeOS isn't maintained anymore (latest version still working
on BeOS was something like 1.0."
WEB: Update credits: Haiku maintained by Luc Schrijvers

Quoth Luc Schrijvers (Begasus) on scummvm-devel:
"Haiku is stepping up and there is a recipe (script to build
scummvm) in the haikuporters git repo [...] I'll still do a
full build and make it available for download that could be
upped on your download page when ready"