kgdb: remove unused HAVE_ARCH_KGDB_SHADOW_INFO config variable

Remove HAVE_ARCH_KGDB_SHADOW_INFO because it does not
exist anywhere in the kernel mainline sources

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

lib/Kconfig.kgdb

@@ -1,7 +1,4 @@
 
-config HAVE_ARCH_KGDB_SHADOW_INFO
-	bool
-
 config HAVE_ARCH_KGDB
 	bool