[chore][receiver/mongodb] Update metric supported versions (open-tele…

…metry#32849)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
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Duplicate of
open-telemetry#32779,
it looks like the other can't be updated properly as it was a PR from a
branch in the `contrib` repo, instead of my own fork.

receiver/mongodbreceiver/README.md

@@ -69,10 +69,6 @@ The full list of settings exposed for this receiver are documented [here](./conf
 The following metric are available with versions:
 
 - `mongodb.extent.count` < 4.4 with mmapv1 storage engine
-- `mongodb.session.count` >= 3.0 with wiredTiger storage engine
-- `mongodb.cache.operations` >= 3.0 with wiredTiger storage engine
-- `mongodb.connection.count` with attribute `active` is available >= 4.0
-- `mongodb.index.access.count` >= 4.0
 
 Details about the metrics produced by this receiver can be found in [metadata.yaml](./metadata.yaml)