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

diff --git a/lib/Kconfig.kgdb b/lib/Kconfig.kgdb
index a5d4b1d..2cfd272 100644
--- a/lib/Kconfig.kgdb
+++ b/lib/Kconfig.kgdb
@@ -1,7 +1,4 @@
 
-config HAVE_ARCH_KGDB_SHADOW_INFO
-	bool
-
 config HAVE_ARCH_KGDB
 	bool