package/heimdal: fix build when the host has some DB libs
When the host has a DB library installed, namely LMDB, host-heimdal
will detect it and try to use, resulting in a build failure due to
missing symbols.
Really disable all the DB backends, we don't need them.
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>