Remove check of not supported keys in RinexLoader
After reading the header of a Rinex observation file, Orekit verifies that all the mandatory keys were parsed. However, some keys are not supported yet and Orekit checks anyway if the key is present in the file. It looks a little bit pretentious...
We always considered that Orekit must be very strict when writing a file but can accept some laxity when parsing a file. Therefore, I propose two options:
(1) Remove the check of the mandatory keys that are not supported by Orekit
(2) Remove the check of all the mandatory keys to be the most flexible possible
Edited by Bryan Cazabonne