quiver's reply is correct. If you are on a Mac, Homebrew as of today (2018-10-22) only installs and upgrades to awscli version 1.16.30; I had to upgrade to version 1.16.38 today to access the delete-transcription-job argument. If you rely upon Homebrew, uninstall all versions of awscli managed by Homebrew with:
$ brew uninstall --force awscli
Then install with pip using:
$ pip3 install awscli
Verify using:
$ aws --version
aws-cli/1.16.38 Python/3.7.0 Darwin/17.6.0 botocore/1.12.28
Your specific version string may vary, only the "aws-cli/1.16.38" part matters of course.