update/drop devcontainer.

[jkowalleck]

https://github.com/CycloneDX/cyclonedx-python/tree/master/.devcontainer
needs some maintenance.

it tries to install dependencies via requirements.txt which is no longer present.
instead poetry is used.

[jkowalleck]

@coderpatros do you think the devcontainer is still needed?
could you describe the usage?

[jkowalleck]

related: #239

[coderpatros]

It basically allows someone to spin up a vscode containerised dev environment. Now that poetry is used I think the need isn't the same. At the time I had trouble getting everything working locally easily.

And if we want an easy option for new contributors I'd go gitpod over vscode devcontainers now.

[jkowalleck]

will remove the docker container for now.
options like gitpod or github.dev might come in the future. - see #264