Summary:
This YB_TODO had a comment above it: `/* Enable this check when contrib directory is enabled in build_postgres.py */`.

The contrib directory was enabled by D36639 / caa16a6fe3b538f787a28236c6659de3681623a0, so it is now
safe to re-enable this check.
Jira: DB-14659

Test Plan: Jenkins

Reviewers: hsunder, fizaa

Reviewed By: hsunder

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D40885