crda: fix check-package warning

In commit 3e79bd3f456cef12886ac6b086c8bc78e3e520f8 ("crda: bump
version to 4.14"), the value of CRDA_SOURCE was changed to use what is
the default value for <pkg>_SOURCE, triggering a warning from
check-package:

package/crda/crda.mk:8: remove default value of _SOURCE variable (http://nightly.buildroot.org/#generic-package-reference)

This commit fixes that by dropping CRDA_SOURCE entirely.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/crda/crda.mk

@@ -5,7 +5,6 @@
 ################################################################################
 
 CRDA_VERSION = 4.14
-CRDA_SOURCE = crda-$(CRDA_VERSION).tar.gz
 CRDA_SITE = https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/crda.git/snapshot
 CRDA_DEPENDENCIES = host-pkgconf host-python-pycrypto libnl libgcrypt
 CRDA_LICENSE = ISC