This reverts commit 7665dcf1bb.
Also revert the related build-sys changes to fix the build.
codegen generated code depends on spice-common code (marshaller,
messages etc), it makes more sense to keep the generator along
this. Otherwise a newer protocol release will fail to build older
projects.
*.proto files are required as well, since it generates code that parent
modules depend on unconditionnaly.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
