the codegen ci workflow was previously fixed by copying the checkout dir
to the GOPATH. With the updated codegen tooling, this alignment is not a
requirement any more.
This simplifies the codegen workflow again by reverting the earlier
changes that added the copy mechanism.
This reverts commit 714f80a80a.
This reverts commit f32d3df995.
Signed-off-by: Michael Adam <obnox@samba.org>