image: Remove the do_package_write_* tasks

image: Remove the do_package_write_* tasks

Now we're filtering tasks in the rpm indexing code so that tasks can only
see the packages they really depend upon, having noexec package_write tasks
around is causing problems since the tasks exist but don't have manifests.

Removing the tasks entirely solves this problem and streamlines the
task execution graph too.

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