Rephrase dialog message of clear storage dialog for security concern am: 6024ea553a am: b0ce558a3e am: 551083020b

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

Change-Id: I29a1c85dfdc3a7b7d1cab6aa79ad147a4328c6c9