Update Secure Source Manager deletion policy comment (#14998)

Author: ericpang777

mmv1/products/securesourcemanager/Instance.yaml

@@ -188,7 +188,7 @@ virtual_fields:
       to be abandoned, rather than deleted. Setting `DELETE` deletes the resource
       and all its contents. Setting `PREVENT` prevents the resource from accidental
       deletion by erroring out during plan.
-      Default is `DELETE`.  Possible values are:
+      Default is `PREVENT`.  Possible values are:
         * DELETE
         * PREVENT
         * ABANDON

mmv1/products/securesourcemanager/Repository.yaml

@@ -98,7 +98,7 @@ virtual_fields:
       to be abandoned, rather than deleted. Setting `DELETE` deletes the resource
       and all its contents. Setting `PREVENT` prevents the resource from accidental deletion
       by erroring out during plan.
-      Default is `DELETE`.  Possible values are:
+      Default is `PREVENT`.  Possible values are:
         * DELETE
         * PREVENT
         * ABANDON