Update Set-Label.md

Per bug below, we are removing reference to this parameter being reserved for internal-only use and adding a brief description.

https://o365exchange.visualstudio.com/IP%20Engineering/_workitems/edit/4496667

Author: maberzin

exchange/exchange-ps/exchange/Set-Label.md

@@ -935,7 +935,7 @@ Accept wildcard characters: False
 ```
 
 ### -LabelActions
-This parameter is reserved for internal Microsoft use.
+The LabelActions parameter is used to specify actions that can be performed on labels.
 
 ```yaml
 Type: MultiValuedProperty