remove appveyor

Removes appveyor as we no longer actively use them as a CI provider for our projects.

GUS Work Item: [@W-9251593][1]

[1]: https://gus.lightning.force.com/lightning/r/ADM_Work__c/a07AH000000LSHBYA4/view

Signed-off-by: Stanley Stuart <[email protected]>

Author: fivetanley