s390: remove unused _ehead symbol

Since startup code now reserves memory ranges [0, PARMAREA_END] and
[_stext, <end of kernel>] _ehead symbol is not used and could be
cleaned up.
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/sections.h

@@ -4,6 +4,4 @@
 
 #include <asm-generic/sections.h>
 
-extern char _ehead[];
-
 #endif

arch/s390/kernel/head64.S

@@ -87,8 +87,6 @@ ENTRY(startup_continue)
 .Llinkage_stack:
 	.long	0,0,0x89000000,0,0,0,0x8a000000,0
 
-ENTRY(_ehead)
-
 #
 # startup-code, running in absolute addressing mode
 #