Remove dependency on units

[mhpob]

Remove dependency on units introduced in a50334a. The same outcome as units::drop_units can be done by coercing to a matrix. Addresses one part of #122.

Running the examples in make_transition3 with and without units::drop_units result in identical objects:

> identical(ex1, ex1_nounits)
[1] TRUE
> identical(ex2, ex2_nounits)
[1] TRUE
> identical(ex3, ex3_nounits)
[1] TRUE

This PR gets glatos down to 20 explicit dependencies, which clears the R CMD check dependency note:

• before: https://github.com/ocean-tracking-network/glatos/actions/runs/8193178738/job/22406314930?pr=223#step:6:66
• now clear: https://github.com/ocean-tracking-network/glatos/actions/runs/9068760018/job/24916782875?pr=229#step:6:66

Current R CMD check failure is due to a floating point issue on macOS which will be fixed with acceptance of #228