Do you have Outlook? You can try to use the Hotmail Outlook connector, thereby syncing your Hotmail to Outlook (via a new profile) and then in theory, deleting your new profile's contacts in Outlook should sync to Hotmail, therefore deleting from Hotmail.
Or, if you don't use the email any more, close the account?
Or, and this is nearly deleting them all at once (depending on how many you have) but is still quite laborious but it does at least offer the ability to do so via the web interface without having Outlook installed.
Sign in to Outlook.com/Hotmail.com
Click on People (on the top left it shows Outlook, click on the drop down arrow to select people)
Here, you can select all the contacts you wish (don't wish) and they will appear on the right side of the screen. Above these, is the option to delete as the group).
It only displays X records at any point so if you've got a lot of contacts, this is probably not ideal.