Summary:
Correct the API notations for PITR delete API

Original commit: 1e2654e608d76a2f66c4e2b09c5a14f56319b7b3 / D41994

Test Plan: `sbt swaggerGen`

Reviewers: skurapati, anabaria

Reviewed By: skurapati

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D41995