Summary:
This reverts changes related to `yb_amiscoveredbymaintable` in b4ef0c523359e3572c2bc3f619780cacf6edbbde and .b9b57c6f791cb9f28d8bec9372e9a433a903980c in line with the most up to date requirements for index co-partitioning. In the previous design, co-partitioned indexes were meant to share almost all metadata and storage with the main table.

The currently implemented design for co-partitioning in docdb creates such indexes a different way. Co-partitioned indexes on creation create new data storage but get colocated with their respective main tables in a mechanism similar to the existing colocation index creation.

This change reverts any remnants of the previous design on the query layer to allow for this redesign.

b9b57c6f791cb9f28d8bec9372e9a433a903980c had a few conflicts with this change that modified some call-sites of `YBIsCoveredByMainTable`.

Test Plan: Jenkins

Reviewers: telgersma, jason, fizaa

Reviewed By: telgersma

Subscribers: yql, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D40340