Conversion fails to strip variable

Running this snippet
```
using PhysicalConstants.CODATA2018: c_0

index = 1.858
c::Float64 = c_0 / index
```
raises

```ERROR: DimensionError: and m s^-1 are not dimensionally compatible.```

It is my understanding that this comes from the fact that ```Float64(c_0)``` returns a ```Unitful.Quantity{Float64, 𝐋 𝐓 ^-1, Unitful.FreeUnits{(m, s^-1), 𝐋 𝐓 ^-1, nothing}}``` instead of a Float64.

I don't think this should be the expected behavior and in such a case the variable should be stripped of its unit.