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

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

Change-Id: I7abb2a4fbc773e78ba750883d44d5a617d764b2c