I found that some files were not getting removed from the sysroot, despite them
clearly being removed by the recipe. I found SYSROOT_DESTDIR is only ever copied
into, not cleaned. This patch ensures its empty when the task starts so that
stale files are removed and not persisted.
(From OE-Core rev: 8a313f6d32ae0bdac0393887712b09f1b685aaa5)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>