Rephrase dialog message of clear storage dialog for security concern am: 6024ea553a am: 2d08d34762 am: ebcc8d976f

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/16101567

Change-Id: I52494118119b95809f32ff33f2cbda406d50e84e