base-files: uci-defaults-new, config_generate: refactor code and drop old vlans

base-files: uci-defaults-new, config_generate: refactor code and drop old vlans

Remove support for now unused ucidef_add_switch_vlan(), move port->vlan and
vlan->interfaces conversion to uci-defaults-new.sh and massively simplify
config_generate.

This change prepares the following upcoming steps:

 * Eliminate use of ucidef_set_interface_lan_wan() for switch only devices
 * Merge ucidef_add_switch() with ucidef_add_switch_ports()

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47719 3c298f89-4303-0410-b956-a3cf2f4a3e73