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.
Last time I remember it increasing visual quality was back around, say, the 3.0-500s. One of the first few issue reports I filed was about EFB scaling not working on EFB to RAM unless you checked "Cache", thus I'm pretty sure the description was based on that bug.

Of course, if caching is somehow supposed to have the possibility of increasing visual quality, I can change it back.