v.io/jiri/profiles: prevent use of target Tags.

This is in preparation for removing Tags altogether.
1. refuse to write out a manifest with Tags and
remove use of Tags in tests.
2. don't use Tags in any tests/examples.

MultiPart: 2/2

Change-Id: I451b345c266c4bd8bb283e4f808f62bfcb3062f5
5 files changed