package/googlefontdirectory: better solution to avoid check-package warning

Rather than tell check-package to ignore a false-positive issue, just
avoid the issue to begin with, by using an intermediate variable to
construct the list of licenses.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>