I assume you are using the remote MSSQL extension , in this case, you can disable the feature set which includes the metric you are not interested in, but it will disable also other metrics in the same feature set. If you need just a single metric, it's not directly possible and you will need to fork the extension and modify it for your purposes.
Sure, documentation is general docs and also developer docs.Anyway first I'd recommend reaching out to email@example.com or your Dynatrace contact - maybe they can consider modifying the extension in future releases.
If you decide to fork, keep in mind, that you will need to modify every update of the upstream extension, you need to deploy your certificate to each of your ActiveGates where the extension runs. Then it involve downloading the extension, modifying it, signing, packaging and deploying back to your environment.