Revert "Reference platform.h by ../src/platform.h - AIX is ignoring -I flags"

This reverts commit 1e8e4d79c885b27831e2196d94987cc2817e0f04.

Turns out my AIX system  was sick somehow and was having issues with the filesystem I was compiling on.  I copied the source to /tmp/ and it worked just fine without this change.