emulators/snes9x-gtk: Update to 1.61; maintain

This port hasn't been updated in almost 6 years, so quite a bit has
changed. See the releases links below for details. Notable changes
include switching to the meson build system and using GTK 3 with
c++ bindings instead of GTK 2.

Some options have been dropped because they are no longer applicable
or are now mandatory.

https://github.com/snes9xgit/snes9x/releases
https://github.com/snes9xgit/snes9x/releases/tag/1.61