[POWERPC] Remove unused __max_memory variable

Remove the __max_memory variable, as it is not referenced anywhere
in the tree besides some code in arch/ppc.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/mm/init_64.c

@@ -72,9 +72,6 @@
 #warning TASK_SIZE is smaller than it needs to be.
 #endif
 
-/* max amount of RAM to use */
-unsigned long __max_memory;
-
 phys_addr_t memstart_addr;
 
 void free_initmem(void)