Remove deprecated android.system.Os.{ioctlInt,sendfile,waitpid}.

These three methods were recently deprecated because their signatures
depend on android.util.Mutable{Long,Int}. A follow-up CL is moving
those classes to framework, which means that they will no longer be
accessible to libcore at compile time.

Bug: 67901714
Test: Treehugger

Change-Id: Iec279d3adc4d8b2337037c277a7e1597e912e16d