chore: use DefaultNetwork instead of duplicate code

[rach-id]

Overview

Remove duplicated code and use directly DefaultNetwork.

Checklist

• New and updated code has appropriate documentation
• New and updated code has new and/or updated testing
• Required CI checks are passing
• Visual proof for any user facing features like CLI or documentation updates
• Linked issues closed with keywords

[rach-id]

2 checks are failing:

• linter for a not working link, issue Fix ADR link failing in CI #1413
• deleting directory issue, which hopefuly can be solved by this: chore: delete testnode home dir during cleanup #1411

[rootulp]

LGTM if all integration tests still pass. Nice clean up 🧹

[evan-forbes]

while a lot of the code is duplicated, the reason for leaving this after we introduced DefaultNetwork was to illustrate what needed to be done to have a test with a custom genesis state.

however we do need to test DefaultNetwork, and we can always reverse engineer DefaultNetwork, so 👍

[evan-forbes]

we can also show how to do a custom genesis state when we #829