Summary:
For src/postgres/src/backend/utils/adt/jsonapi.c, YB historically
imports upstream PG commits

- 73ce2a03f30b52d6bfb26bc28f1e3e1aa1637577
- 1f3a021730be98b880d94cabbe21de7e4d8136f5
- 530609aa4263bee5b5ca205d83f0dbad098d0465
- 11b5e3e35d3900164cb36754ee4e4dcab0bd02f0

and does a PG 15.2 merge, the main commit being
55782d561e55ef972f2470a4ae887dd791bb4a97.
55782d561e55ef972f2470a4ae887dd791bb4a97 comments out the entire
src/postgres/src/backend/utils/adt/jsonapi.c with an #ifdef NEIL.  And
that works because upstream PG beb4699091e9fab1c5f465056bef35c9ddf7f9fc
moves this file to src/common/jsonapi.c, and
55782d561e55ef972f2470a4ae887dd791bb4a97 already brings in upstream PG
src/common/jsonapi.c with no changes.  So the correct resolution here is
to delete the old src/postgres/src/backend/utils/adt/jsonapi.c (and
remove it from the corresponding Makefile).  The previous point imports
are irrelevant since they are already contained in PG REL_15_2 and YB
did not make any adjustments to jsonapi.c.

Jira: DB-15701

Test Plan:
Close: #26351
Jenkins: compile only

Reviewers: aagrawal, fizaa

Reviewed By: aagrawal

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D42438