Rephrase dialog message of clear storage dialog for security concern am:...

Rephrase dialog message of clear storage dialog for security concern am: 881d7ec5 am: 0549b8c4 am: 82872a85 am: 3424ff2b

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

Change-Id: Idc5cb5e0f3530922e521b4c58b224d89f9f2bb1b