Remove default components and milestones in `trac-admin initenv`

[anonymous]

When initializing a new environment it will be populated with placeholder components and milestones (ie "component#" and "milestone#").

However I think it's rather unlikely that these actual components and milestones will be useful in an actual project. This means that the next step is likely to manually remove these components and milestones and populate the environment with relevant components and milestones.

I suggest that trac-admin initenv instead create an environment without any components or milestones predefined or if required prompt the user for the actual names of the components and milestones.