Rephrase dialog message of clear storage dialog for security concern am: 881d7ec5ab am: 0549b8c4e3

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/16101566

Change-Id: I0a46c89f3a211f7b937c44b77c08f85d04ef8155