CDRIVER-4556 Remove use of `collStats` (#1249)

* sync specification tests to commit 6632b7606e74c6e83ee2d80b7571f55485c7ff33

* remove runCommand Example 2

The example removed from DRIVERS-448.

* suggest $collStats in mongoc_collection_stats

* move example in mongoc_collection_command_simple to example source

* add missing declaration of `str`

* use `ping` instead of `collStats` command

* move Executing Commands code to example

* replace `collStats` with `ping`

* use `mongoc_client_command_simple`

To simplify the example.
There is no need to run the command with the mongoc_collection_t handle.

* remove note about returning cursors

`mongoc_collection_command`, `mongoc_database_command` and `mongoc_client_command` return a cursor. They are documented as `superseded` by other helpers.

* skip test using collStats on servers > 6.0

* remove redundant captions

Co-authored-by: Ezra Chung <88335979+eramongodb@users.noreply.github.com>

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Co-authored-by: Ezra Chung <88335979+eramongodb@users.noreply.github.com>