Please add a delete instruction for build recipes

[Darxus]

https://code.launchpad.net/~darxus/+recipe/linux-firmware-amdgpu-daily-focal

In this PPA, I delete the amdgpu directory, and nest-part the latest version from upstream. It seems the only way to delete a directory is to clone the repo, delete the directory, push that repo onto launchpad, then merge it.

Which breaks, if the files change in the base repo. So the same repo merge doesn't work for different ubuntu releases.

I had a similar problem with daily builds of spamassassin. Upstream source had a debian directory, so I needed to start off with merging a repo that deletes that directory.

This seems like a common problem, which would be much more simply and cleanly handled with a delete instruction.