[MS24] Remove FileUtils.sync dependencies

FileRotator will be built with Connectivity mainline module
while the file location will be kept inside platform.
Thus, hidden api usage needs to be addressed.

This change removes some dependencies by inlining the content
of FileUtils.sync to remove the dependency, and change the
Slog to Log.

Test: TH
Bug: 204830222
Change-Id: I6105850dd8311072fd8de2e2864d11fdb052f061