vinyl: zap vy_mem_update_formats

A piece of code left from the inglorious past, which doesn't even have
a forward declaration, let alone used anywhere. Remove it.

src/box/vy_mem.c

@@ -123,19 +123,6 @@ vy_mem_new(struct vy_mem_env *env, int64_t generation,
 	return index;
 }
 
-void
-vy_mem_update_formats(struct vy_mem *mem, struct tuple_format *new_format,
-		      struct tuple_format *new_format_with_colmask)
-{
-	assert(mem->count.rows == 0);
-	tuple_format_unref(mem->format);
-	tuple_format_unref(mem->format_with_colmask);
-	mem->format = new_format;
-	mem->format_with_colmask = new_format_with_colmask;
-	tuple_format_ref(mem->format);
-	tuple_format_ref(mem->format_with_colmask);
-}
-
 void
 vy_mem_delete(struct vy_mem *index)
 {