build(python): remove python 3.7 from kokoro Dockerfile#16

gcf-merge-on-green[bot] merged 2 commits intomastergoogleapis/python-appengine-logging:masterfrom

owl-bot-update-lock-5ff7446edeaede81c3ed58b23a4e76a5403fba1350ce28478045657303b6479dgoogleapis/python-appengine-logging:owl-bot-update-lock-5ff7446edeaede81c3ed58b23a4e76a5403fba1350ce28478045657303b6479dCopy head branch name to clipboard