Cleanup userspace/*

1. Delete attic/* and shared.[ch] (shared.[ch] were previously moved to
switch.[ch])
2. Remove SWCFG_SETIFDESC from cmd_if_desc.
3. Rename shared_* functions to switch_*.
Still need to check if build_config.c functionality was entirely ported to
cfgbuild/cfgbuild.c before deleting it.

Signed-off-by: Andreea Hodea <hodea_andreea@yahoo.com>