Clobber the uapi ion.h with the old ion.h until Android switches to the new ABI.

Internal master is already switched, but that looks too painful to cherrypick
into AOSP, so let's hack AOSP back to pre-uapi for this one file. I'll revert
this immediately in internal master (where the current situation is that the
old headers have been clobbered with uapi headers).

Bug: 11859767
Change-Id: Ie6d7df965c497f8853cf3d3c2187a93e6992ad15