[fluidsystems] Reuse brine fluid system in BrineCO2

See BrineAir for this can be achieved. Check if the binary laws Brine_CO2 are actually needed.

mentioned in issue #474 (closed)

mentioned in merge request !1153 (merged)

closed via commit 2b32fdb9

closed via merge request !1153 (merged)

mentioned in commit 2b32fdb9