staging: android: ion: Remove system heap aliasing

Now that all clients have transitioned to using the correct
system heap ID, remove the aliasing logic that reroutes
allocations from ION_HEAP_SYSTEM to ION_SYSTEM_HEAP_ID.

For now, print a warning if an allocation is directed
towards ION_HEAP_SYSTEM to catch anyone who is still using
ION_HEAP_SYSTEM.

Change-Id: Ie4a7c6384806016cc62837b14f4bc8d05cd1549d
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>