The only difference between artificial-consciousness and self-awareness is that the former is "restricted to engineered artifacts", so I think these tags should be merged and only the tag artificial-consciousness should exist, given that "restricted to engineered artifacts" does not deserve its own tag on a website related to the theoretical and philosophical aspects of AI.
Self-awareness has a lot of usage in general, and I don't think it's entirely synonymous. Consciousness, in the most basic definition, is merely awareness of an environment.
Additionally, non-artificial intelligences (humans) have self-awareness. So it's useful to be able to distinguish.