s390/setup: Drop stale ident_map_size declaration

ident_map_size is no longer a standalone variable and the declaration
in asm/setup.h conflicts with its current definition in asm/page.h
introduced with commit 236f324 ("s390/mm: Create virtual memory
layout structure"). Remove the stale declaration.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: Vasily Gorbik

arch/s390/include/asm/setup.h

@@ -52,7 +52,6 @@ extern unsigned int zlib_dfltcc_support;
 #define ZLIB_DFLTCC_INFLATE_ONLY	3
 #define ZLIB_DFLTCC_FULL_DEBUG		4
 
-extern unsigned long ident_map_size;
 extern unsigned long max_mappable;
 
 /* The Write Back bit position in the physaddr is given by the SLPC PCI */