Remove the `using pre-built Docker containers` section from Quickstart guide

[yczhang-nv]

Description

Removing the using pre-built Docker containers section from Quickstart guide.

Currently the pre-built container is not able to launch a triton server inside the container, and installing docker inside docker is not preferable. However, anyone using a pre-built container only has access to the models inside the container, and they are not able to use the models on triton server that runs outside of the container. Therefore, we stop recommending pre-built container in the quickstart guide at this moment.

Closes #1507

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• When the PR is ready for review, new or existing tests cover these changes.
• When the PR is ready for review, the documentation is up to date with these changes.