buildroot

package/systemd: Remove systemd-bootchart

Since systemd v230, bootchart has been removed from the source of
systemd and now lives in its own repository.
A new package will be added in the next commit.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>