package/nodejs: remove support for express

BR2_PACKAGE_NODEJS_MODULES_EXPRESS has been deprecated.  To continue using
add express to BR2_PACKAGE_NODEJS_MODULES_ADDITIONAL

Fixes:
http://autobuild.buildroot.org/results/fcfa38e98c22c8809452f7d0ee86dfe2e9d2482f
http://autobuild.buildroot.org/results/946996fa78c7814d1e0ea0ef1239c6eb0c7aa8dd
http://autobuild.buildroot.org/results/df920e7b17617f1e4867d94eda52cab38f7b0622



Signed-off-by: Martin Bark <martin@barkynet.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>