Mask tool missing in premiere pro

As Shebbe mentioned, Masking has been updated in Beta. You will now find new Masking tools in the Tools panel. To create an Opacity Mask, select Opacity in th ECP, then select one of the Mask Tools in Tools panel and then create a Mask in the Program Monitor.

More information is provided in the link Shebbe shared.

Not removed, new functionality.

https://community.adobe.com/t5/premiere-pro-beta-discussions/now-in-premiere-pro-beta-new-masking-tools/td-p/15484479