remove TimeScale as input from DateUtils functions

Currently the function DateUtils.toJulianDate() that converts an orekit AbsoluteDate to a cesium JulianDate requires a TimeScale input to perform the conversion. However, it is possible to remove this input by using the AbsoluteDate.getJD() function and remembering that the JD return value is in UTC. Submitting this issue to connect it to the MR that simplifies this input function and rewrites the code to accommodate its removal.