Don't enable snapshots by default as they're horrendously unreliable

Do snapshots actually work at all in the latest Android SDK or platform versions?

The Android folk really seem to have given up on making this actually stable, which is annoying. Since I made snapshots default to "on" a long time ago, this is probably screwing up builds for people.

Plus the snapshot functionality is arguably not required now that we have super-speedy x86 images...