sstate: Fix an error handling the taskname

Looking at the code, its clear 'task' is meant not to have the do_ prefix,
however its also clear it can be left in through some code paths.

One result of this can be files not being cleaned from the sysroot correctly.

Fix this.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
sstate: Remove name sstate parameter

A while ago we stopped supporting sstate names which were different from the
taskname. This patch finishes cleaning up some code remnants from that
which were causing data duplication and confusion.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
siteconfig: Unbreak after sstate changes some time ago

Some time ago, the sstate name field was dropped. This code wouldn't have
worked since then. Makes me wonder if we really need it.

Anyhow, my last patch properly breaks it. This fixes the naming so
it works as designed again.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>