Bigtable latency testing with retry changes in Gapic layer

[danieljbruce]

Another test for latency in Bigtable. Removes parameters that will set the retry properties and relies on retries set in a lower level.

[generated-files-bot[bot]]

Warning: This pull request is touching the following templated files:

• .kokoro/conformance.sh - .kokoro files are templated and should be updated in synthtool