move declarations of tls setup/access functions to pthread_impl.h

it's already included in all places where these are needed, and aside
from __tls_get_addr, they're all implementation internals.

src/thread/__tls_get_addr.c

@@ -2,8 +2,6 @@
 #include "pthread_impl.h"
 #include "libc.h"
 
-hidden void *__tls_get_new(tls_mod_off_t *);
-
 void *__tls_get_addr(tls_mod_off_t *v)
 {
 	pthread_t self = __pthread_self();

src/thread/pthread_create.c

@@ -178,8 +178,6 @@ static void init_file_lock(FILE *f)
 	if (f && f->lock<0) f->lock = 0;
 }
 
-void *__copy_tls(unsigned char *);
-
 int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)
 {
 	int ret, c11 = (attrp == __ATTRP_C11_THREAD);