Policy webUI: Change wording for merged policies source to 'Merged'

Bug: 990538
Change-Id: I8707e2b3dbf4083460f4e5bbe52b35d95bd26b02
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1746646Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Commit-Queue: Yann Dago <ydago@chromium.org>
Cr-Commit-Position: refs/heads/master@{#686425}

components/policy_strings.grdp

@@ -407,7 +407,7 @@ Additional details:
     Cloud
   </message>
   <message name="IDS_POLICY_SOURCE_MERGED" desc="Indicates that the policy is a merged values from multiple sources.">
-    Platform and Cloud
+    Merged
   </message>
   <message name="IDS_POLICY_SOURCE_ACTIVE_DIRECTORY" desc="Indicates that the policy originates from a local server, e.g. Samba or Active Directory.">
     <ph name="MICROSOFT_ACTIVE_DIRECTORY">Local Server</ph>