remove redundant type signature in gu/seq.h

src/runtime/c/gu/seq.h

@@ -108,9 +108,6 @@ gu_buf_flush(GuBuf* buf);
 #define gu_buf_pop(BUF, T)			\
 	(*(T*)gu_buf_trim(BUF))
 
-void
-gu_seq_resize_tail(GuSeq seq, ptrdiff_t change);
-
 void
 gu_buf_sort(GuBuf *buf, GuOrder *order);