KIJIMR-4. Remove org.kiji.mapreduce.tools.RequiredFlagException

This commit removes RequiredFlagException from kiji-mapreduce, because
it already exists in kiji-schema.  All usages of this exception in
kiji-mapreduce have been modified to depend on the class in kiji-schema.

Signed-off-by: Christophe Taton <taton@wibidata.com>