Update Clear-MobileDevice.md

My change to the -AccountOnly switch description is because of https://o365exchange.visualstudio.com/O365%20Core/_workitems/edit/1082043

I clarified with the Adam Ding that the change just ignores -AccountOnly, because the switch is not needed (and doesn't work) against the new Outlook DeviceType. I also tested and confirmed that performing Clear-MobileDevice for the Outlook DeviceType only removes the specific account's data from Outlook even without -AccountOnly present.

Author: rroddy24

exchange/exchange-ps/exchange/devices/Clear-MobileDevice.md

@@ -154,7 +154,7 @@ Accept wildcard characters: False
 ```
 
 ### -AccountOnly
-The AccountOnly switch specifies whether to perform an account-only remote device wipe where only Exchange mailbox data is removed from the device. You don't need to specify a value with this switch.
+The AccountOnly switch specifies whether to perform an account-only remote device wipe where only Exchange mailbox data is removed from the device. You don't need to specify a value with this switch. Note that this switch is not needed when executing the command against a DeviceType of Outlook, as for the Outlook DeviceType, only the account is removed whether this switch is present or not.
 
 ```yaml
 Type: SwitchParameter