ANDROID: staging: ion: Remove unnecessary ion heap ops

The heap operations are redundant now that we have default
dma_buf operations. So, remove them.

Bug: 133508579
Bug: 140290587
Test: ion-unit-tests

Change-Id: I8f87c22896e128f48ed222421cabc23ab238ff69
Signed-off-by: Sandeep Patil <sspatil@google.com>