Removed serialization for attitude providers.

src/changes/changes.xml

src/main/java/org/orekit/attitudes/AttitudeProvider.java

src/main/java/org/orekit/attitudes/AttitudesSequence.java

src/main/java/org/orekit/attitudes/BodyCenterPointing.java

src/main/java/org/orekit/attitudes/CelestialBodyPointed.java

src/main/java/org/orekit/attitudes/FixedRate.java

src/main/java/org/orekit/attitudes/GroundPointing.java

src/main/java/org/orekit/attitudes/InertialProvider.java

src/main/java/org/orekit/attitudes/LofOffset.java

src/main/java/org/orekit/attitudes/LofOffsetPointing.java

src/main/java/org/orekit/attitudes/NadirPointing.java

src/main/java/org/orekit/attitudes/SpinStabilized.java

src/main/java/org/orekit/attitudes/TabulatedLofOffset.java

src/main/java/org/orekit/attitudes/TabulatedProvider.java

src/main/java/org/orekit/attitudes/TargetPointing.java

src/main/java/org/orekit/attitudes/YawCompensation.java

src/main/java/org/orekit/attitudes/YawSteering.java

...rg/orekit/gnss/attitude/AbstractGNSSAttitudeProvider.java

src/main/java/org/orekit/gnss/attitude/BeidouGeo.java

src/main/java/org/orekit/gnss/attitude/BeidouIGSO.java