Rephrase dialog message of clear storage dialog for security concern am: 7d22136f am: 337e182e am: d67d983b am: 41e6a117 am: 43d833ae am: f0cc223e am: 11ac83dc

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/16101568

Change-Id: Ibc77c5994210dfa21da0578d9f6c87847fe3ea2d