Remove 'stderr' validation from 'Prune Journal Log'

AES may fail stderr check where it expects "Vacuuming done".
This text is not guaranteed to be found.

Change-Id: I174b58382daa1b5697c8d454a97f2fc4e5ad63f9
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/lib/utils.robot b/lib/utils.robot
index 66bf1ec..21a073e 100755
--- a/lib/utils.robot
+++ b/lib/utils.robot
@@ -691,7 +691,6 @@
     ...  return_stderr=True  return_rc=True
 
     Should Be Equal  ${rc}  ${0}  msg=${stderr}
-    Should Contain   ${stderr}  Vacuuming done
 
 Set BMC Power Policy
     [Documentation]   Set the given BMC power policy.