exp init: hide message about workspace tree on --explicit

[skshetry]

On --explict, it displayed no worktree at all, as exp init does not know about default paths:

$ dvc exp init -if --explicit
This command will guide you to set up a default stage in dvc.yaml.
See https://dvc.org/doc/user-guide/project-structure/pipelines-files.

Command to execute: test

Enter the paths for dependencies and outputs of the command.
DVC assumes the following workspace structure:

Path to a code file/directory [n to omit]:

The message "DVC assumes ..." won't be shown now on the explicit mode.

Part of #6446.

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Thank you for the contribution - we'll try to review it as soon as possible. 🙏