[terraform] Making user created vpc false by default

Summary:
We reintroduced user created vpcs as Ashoat's config was on it. This allowed us to avoid mariadb downtime by not having to force a move to the default vpcs.

We expect users to use the default vpcsso user created vpc should be false by default

Depends on D12875

Test Plan: terraform plan. No longer have to specify user created vpc

Reviewers: varun, bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12876