Improve explanation of passive zones

Currently the explanation for passive zones says that they "are not used as location for device trackers" which is misleading and does not fit the second sentence that says: "This is useful if you just want to use it for automations.

This commit clarifies that by changing to "not shown as" and fixes the plural / singular mismatch between the two sentences.

src/translations/en.json

@@ -4491,7 +4491,7 @@
             "latitude": "Latitude",
             "longitude": "Longitude",
             "passive": "Passive",
-            "passive_note": "Passive zones are hidden in the frontend and are not used as location for device trackers. This is useful if you just want to use it for automations.",
+            "passive_note": "Passive zones are hidden in the frontend and not shown as a location of people or device trackers. This is useful if you just want to use them for automations.",
             "required_error_msg": "This field is required",
             "delete": "Delete",
             "create": "Create",