remove unused bsc_copyright from bsc_vty.c

Change-Id: I281791c0f57ca75ffe14431a3030811b2d224f0b
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index f856e30..5c95e85 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -4027,7 +4027,6 @@
 }
 
 extern int bsc_vty_init_extra(void);
-extern const char *openbsc_copyright;
 
 int bsc_vty_init(const struct log_info *cat)
 {