Remove Non Required Package from Dockerfile.

[azusa]

I guess these two packages( apt-transport-https and gnupg2 ) are to use when users add a external apt repositories in Dockerfile . Codes could run without these packages.
So these packages are non required for the example purpose.

[Chuxel]

We're trying to keep this in sync with the core vscode-dev-container definitions. These keep a common set of packages to make working in the dev containers easy. They're not intended for production, but can be referenced in a multi-stage dockerfile if you want to have a production verses development image.