take out orphan externs (empty_string/slash_string)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/dcache.h

@@ -56,9 +56,7 @@ struct qstr {
 
 #define QSTR_INIT(n,l) { { { .len = l } }, .name = n }
 
-extern const char empty_string[];
 extern const struct qstr empty_name;
-extern const char slash_string[];
 extern const struct qstr slash_name;
 
 struct dentry_stat_t {