Keep using the same version of rand crate

This change is no-op, just renaming an existing 3p dep.

Rand is being updated to the latest version. In the meantime, point
existing users to the soon-to-be previous version.

Bug: 420420630
Test: treehugger
Flag: EXEMPT: dependency rename, external library
Change-Id: I71a759f642fca1fdf74b5970b40a484929e01c85