remove superfluous --with-theme=default option

- currently mapped to --with-theme=galaxy for migration
- warns though

Change-Id: Ib40dabd4c54b6cac0b7f3c6f6183b2e4d1545331
remove special casing for obsoleted default theme

Change-Id: I6688251eac8ecb5ea671cae281c2445df773be16
remove special casing for default theme in vcl

Change-Id: I4d7a37ab9b31fcce7704f07d883d6f7806f066ec