Trim SGX-specific packages from playbooks

[eddyashton]

Follow-up to #6447. Changing defaults and updating docs to simplify install for SNP/virtual.

[achamayou]

@eddyashton one thing to be careful with is clang-format.

We've deliberately hardcoded 11 to keep things stable. Right now we still cut CI images from release/5.x, and that still installs clang-format-11 no matter what.

I don't think we will be able to do that on Azure Linux 3.0 (default there is clang-18), so we will have to work out what the transition looks like.

[eddyashton]

@eddyashton one thing to be careful with is clang-format.

We've deliberately hardcoded 11 to keep things stable. Right now we still cut CI images from release/5.x, and that still installs clang-format-11 no matter what.

I don't think we will be able to do that on Azure Linux 3.0 (default there is clang-18), so we will have to work out what the transition looks like.

We should update to a more recent clang-format at some point. But probably after we're cutting from main again. The current diff when formatting with my clang-format-18 isn't too obscene, 19 files touched, just new opinions on where we split lines/allow whitespace. Could potentially minimise that diff further with a different .clang-format, but none of the new options are obvious culprits.