nasmlib: Drop unused seg_init

The helper has been eliminated in 2c4a4d5810

https://bugzilla.nasm.us/show_bug.cgi?id=3392461

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

include/nasmlib.h

@@ -188,10 +188,8 @@ int64_t readnum(char *str, bool *error);
 int64_t readstrnum(char *str, int length, bool *warn);
 
 /*
- * seg_init: Initialise the segment-number allocator.
  * seg_alloc: allocate a hitherto unused segment number.
  */
-void pure_func seg_init(void);
 int32_t pure_func seg_alloc(void);
 
 /*