datastore: remove unused import
datastore: remove unused import

Change-Id: If321e2a7550cede2a9e5ae30340ba50724f30bac
Reviewed-on: https://code-review.googlesource.com/24730
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go