bigtable/bttest: remove noisy log line from inmem
bigtable/bttest: remove noisy log line from inmem

See an example of this flooding the output:
https://travis-ci.org/GoogleCloudPlatform/gcloud-golang/jobs/141500054

Change-Id: I75e32d743a7687e5d637cef3f0136dc79b53054b
Reviewed-on: https://code-review.googlesource.com/5130
Reviewed-by: David Symonds <7f6bb564ed9e580d4f0aa90d53b34578e5d24cb9@golang.org>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,michael-grosshans/google-cloud-go,michael-grosshans/google-cloud-go