Remove some stale @todo doc comments.

Signed-off-by: Russell Steicke <russells@adelie.cx>
Only run one display segment at a time.

Because the power source may be a CR2032, we may have limited current
available - about 3mA.  So only power one display segment at a time to
avoid drawing much more than this.

Signed-off-by: Russell Steicke <russells@adelie.cx>