Change default sim to run on Purdue GP track world

[alanssitis]

Brief Description

Removed tb3 world simulation from Nav2 defaults and added Purdue GP track as the default sim world.

Related Issues

Opens #10

Details

Deleted files attached to the default sim. Added and modified files to use new Purdue GP track.

Tasks

• [x] Updated Documentation

[alanssitis]

Looks like everyone in integration got it working. Merging branch.