Pivot out of the repository so that we test the wheel.

Change-Id: Ie291a4c1f1e847d9ffb86112df027cc6bc2100c2
Reviewed-on: https://code-review.googlesource.com/c/re2/+/63290
Reviewed-by: Alex Chernyakhovsky <achernya@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>