[Merge] ~toabctl/livecd-rootfs:jammy-fix-snap-validate-seed into livecd-rootfs:ubuntu/jammy

[John Chittum]

I'm going to break this into a slightly different statement:

the issue is that the 5.15 kernel does not have ipc/posix_mqueue as a feature. so having the directory added in an earlier step, because the 5.19 kerne is installed at that point, causes the mismatch. 

Break down a slightly different case:

the "generic" directory has `ipc/posix_mqueue`. Kernel-1 does not have the feature. How does Kernel-1 remove the feature?

This change doesn't do that -- it restores "generic" state, which may still be incorrect compared to $KERNEL. The function only allows for addition.

>From a CPC standpoint, we can try a different statement from our end -- only run the snap_validate_preseed at the very end of an end-build. This is arising in EC2 because there's a staged build setup -- a bunch of common steps are performed in one hook, and then the output is passed on. We should only call snap_validate_preseed before the final creation of a deployable artifact. that may change the inheritance structure for specific builds a bit.
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https://code.launchpad.net/~toabctl/livecd-rootfs/+git/livecd-rootfs-1/+merge/445180
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