fix: remove depth from count operation types (#15356)

The `payload.count`, `payload.countVersions` and
`payload.countGlobalVersions` operations accepted a `depth` argument,
but this value is never used in the count logic. Having it show up in
auto-suggestions can be confusing for users (as I just experienced),
since it raises the question of why a count operation would need a depth
at all.

This PR removes the unused depth property