stamp-base was only ever used by the shared workdir code in gcc. This
turned out to be problematic and has been replaced by other approaches
which don't need specialist bitbake knowledge.
stamp-base will likely get removed from bitbake but for now, remove it
from archiver to simplfy the code since gcc no longer uses it.
This stops people getting confused by the obsolete code paths which I'm
getting a lot of questions about.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
