lib: remove extraneous exports and function prototypes

Remove the function prototype for the function
alloc_from_memory_pool() (this function was never implemented).
The function mem_type_to_memory_pool() was not intended to be
exported, so remove the export and function prototypes.

Change-Id: Iac47d5c8a8aaf21554c2a7a56f42d6f7de689d3e
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>
(cherry picked from commit fe7d2ee21af00476fe9e578fcfea1c34a70bd30f)