Remove DataAlreadyRegisteredException

This exception was previously thrown by buildAndRegister method.
After the data API refactor the exception is unused and never thrown.
Remove the exception and update the documentation

Author: ImMorpheus

src/main/java/org/spongepowered/api/data/DataAlreadyRegisteredException.java

@@ -239,7 +239,6 @@ interface Builder extends org.spongepowered.api.util.Builder<DataRegistration, B
          *     in this registration
          * @throws IllegalStateException If there are no {@link DataProvider}s
          *     or {@link DataStore}s, resulting in the keys being dynamic
-         * @throws DataAlreadyRegisteredException If a key has already been claimed by another registration
          */
         @Override
         DataRegistration build();