Summary:
Timeline of events:
 - D36588 introduced an optimization to perform index updates in-place.
 - D38763 gated this feature behind a GUC
 - D39430 fixes an index inconsistency issue with in-place index updates, as discovered by GH-24313.

This revision disables the in-place index updates feature until pending index inconsistency issues can be fixed.
Jira: DB-13744

Test Plan:
```
./yb_build.sh debug --java-test 'org.yb.pgsql.TestPgRegressUpdateOptimized#schedule'
```

Reviewers: smishra

Reviewed By: smishra

Subscribers: smishra, yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D39522