Remove IoUtils from intra-core API

IoUtils was previously used by Conscrypt, but is no longer, as
Conscrypt switched to using its own implementation of the same
methods.  It still needs to be core platform API, because it's used by
a number of frameworks classes.

Bug: 123738844
Test: make checkbuild
Change-Id: I4d734115339cf60c45b109baa9496858d9b4e11c
2 files changed