ion: msm: remove redundant function

Remove a function that results in redefinition errors
when CONFIG_ION_MSM and CONFIG_ION are disabled.
These functions should be placed in
/include/soc/secure_buffer.h

CRs-Fixed: 1058359
Change-Id: I380d68a80d0d3a78f1e7662f2965ed4e8c46a634
Signed-off-by: Clyde Byrd III <cbyrd@codeaurora.org>