Normalize the `BUILD` file licenses comments.

tensorflow_federated/python/research/analytics/BUILD

tensorflow_federated/python/research/baselines/emnist/BUILD

...orflow_federated/python/research/robust_aggregation/BUILD

tensorflow_federated/python/research/semi_cyclic_sgd/BUILD

tensorflow_federated/python/research/simple_fedavg/BUILD

tensorflow_federated/python/research/utils/BUILD

tensorflow_federated/python/simulation/BUILD

tensorflow_federated/python/simulation/datasets/BUILD

tensorflow_federated/python/simulation/models/BUILD

tensorflow_federated/python/tensorflow_libs/BUILD

tensorflow_federated/tools/development/BUILD

third_party/BUILD

third_party/six.BUILD

third_party/zlib.BUILD