Revert "ANDROID: Export dma_heap_add to modularize heaps"

This reverts commit 38f5fe50.

This is no longer needed as upstream is exporting this symbol in commit
a6ccb03f ("dma-buf: dma-heap: export declared functions").

Change-Id: I0b06ff6fd4bef6ab53f597150ab952b421b73041
Signed-off-by: Carlos Llamas <cmllamas@google.com>