Update some setting descriptions in the graphics options. Hide "Disable Destination Alpha" from wx UI.

More than a few of these have annoyed me for a while, what with their typos and odd wording and occasional lack of important details.

Criticisms welcome. I mean, as long as it doesn't devolve into MORE bikeshedding. Even I don't enjoy that.
We don't actually say "XFB" anywhere else in the UI, thus people get confused when told to check Virtual/RealXFB. I agree that the "EFB" one's more unnecessary, though – I just did it for consistency.