ntoskrnl/mm/, MmFreeMemoryAreaByPtr(): remnant declaration since r48999

MmFreeMemoryAreaByPtr search

reactos/ntoskrnl/include/internal/mm.h

 519 MmFreeMemoryAreaByPtr(

MmFreeMemoryAreaByPtr pickaxe:
MmFreeMemoryAreaByPtr() was
defined and used in r12728 (by navaraf)
then
progressively unused
then
removed but not undeclared in r48999 (by "sir_richard")

Let's undeclare it.