CameraService: Use intended iterator when getting remapped keys

- Use the correct iterator to access elements when checking for
removal of keys remapped by RotationAndCrop mappers. Currently, the
iterator for distortionMappers is inaccurately being used for this
check.

Bug: 270474475
Test: CTS test
Change-Id: I095b03d284c49a94c70dd269f634d195ee3fb308