looking-glass-client: enable support for opengl by default

doesn't add any additional dependencies, so there is not really a reason
to disable it.

pkgs/applications/virtualization/looking-glass-client/default.nix

···
 , pulseaudio
 , libsamplerate
 
-, openGLSupport ? false
+, openGLSupport ? true
 , xorgSupport ? true
 , waylandSupport ? true
 , pipewireSupport ? true