move stage3_func typedef out of shared internal dynlink.h header

this interface contract is entirely internal to dynlink.c.

ldso/dynlink.c

@@ -107,6 +107,8 @@ struct symdef {
 	struct dso *dso;
 };
 
+typedef void (*stage3_func)(size_t *);
+
 static struct builtin_tls {
 	char c;
 	struct pthread pt;

src/internal/dynlink.h

@@ -96,7 +96,6 @@ struct fdpic_dummy_loadmap {
 #define DYN_CNT 32
 
 typedef void (*stage2_func)(unsigned char *, size_t *);
-typedef void (*stage3_func)(size_t *);
 
 hidden void *__dlsym(void *restrict, const char *restrict, void *restrict);