Update deletecontact.md

[turgutersozmobitek]

Updated this api req paramater the original parameter.

[whmcs-smueller]

Hello @turgutersozmobitek

Thank you for your contribution and bringing this documentation flaw to our attention.

The api documentation is automatically generated internally and as such, I have opened an internal case (CORE-18497) to have the incorrect parameter name corrected.

Thanks again!