Coordinates should accept a single unit value to apply to all parameters

Consider this code:

    from astropy.coordinates import Angle, ICRSCoordinates
    import astropy.units as u
    
    c = ICRSCoordinates("00 00 06.56343	+25 53 11.2528", unit=u.degree)

I think it’s obvious in this context that the “degree” unit should be applied to both the ra and dec coordinates. The explicit `(u.degree, u.degree)` should only be necessary if each coordinate is different, e.g. `(u.hour, u.degree)`.