Rephrase dialog message of clear storage dialog for security concern am: 7fd0ece6f4 am: 204f82d6c4 am: ac38fc7f32 am: 70b7658b74 am: 0e77ce80cb

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/16101569

Change-Id: I3fd55a6c9d7f50ded696df3fbde5f37df0859aa9