fix: Remove powershell_alternate_hosts from PR

Remove a rule using Host Application (which may or may not exist,
based on the log parser) from the PR. A future PR will clean up
rules using Host Application.

rules/windows/powershell/powershell_alternate_powershell_hosts.yml

@@ -19,7 +19,10 @@ falsepositives:
 level: medium   
 detection:
     filter:
-        ContextInfo: 'powershell.exe'
+        - ContextInfo: 'powershell.exe'
+        - Message: 'powershell.exe'
+        # Both fields contain key=value pairs where the key HostApplication is relevant but
+        # can't be referred directly as event field.
     condition: selection and not filter
  
 ---