gpu: ion: delete ion_system_mapper.c

The mapper abstraction layer was removed before the initial ion
commit, but a stray ion_system_mapper.c file was left in.  Delete
it.

Change-Id: I0001d1ea1b866ebd7ec1306e94472c67a094855f
Signed-off-by: Colin Cross <ccross@android.com>
Git-commit: 3922298f52d193d5e014bf4d28e423cf7bd0b50e
Git-repo: http://android.googlesource.com/kernel/common/


Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>