scripts/make-release: Stop shipping u-boot source as a tarball

scripts/make-release: Stop shipping u-boot source as a tarball

In commit d0dead3b6df7f6cd970e we changed to shipping the u-boot
sources as a tarball, to work around a problem where they
contained a file and directory that had the same name except
for case, which was preventing QEMU's source tarball being
unpacked on case-insensitive filesystems.

In commit f2a3b549e357041f86d7e we updated our u-boot blob
and sources to v2019.01, which no longer has this problem,
so we can finally remove our workaround (effectively
reverting d0dead3b6df7f6cd970e).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Message-id: 20190314155628.8822-1-peter.maydell@linaro.org