package: remove the default value of the $(PKG)_SOURCE variable

Signed-off-by: Jerzy Grzegorek <jerzy.grzegorek@trzebnica.net>
Acked-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com)
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
93 files changed