runtime: remove some unused variables/declarations from runtime.h

Small patch from Eric Botcazou.
    
    Reviewed-on: https://go-review.googlesource.com/34029

From-SVN: r243424

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-2102112e26a21589455f940ec6b409766d942c62
+08d221726e3f50cb197a931ba385fac67f66a028
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/runtime.h

@@ -212,10 +212,6 @@ extern bool runtime_copystack;
 #define USED(v)		((void) v)
 #define	ROUND(x, n)	(((x)+(n)-1)&~(uintptr)((n)-1)) /* all-caps to mark as macro: it evaluates n twice */
 
-byte*	runtime_startup_random_data;
-uint32	runtime_startup_random_data_len;
-void	runtime_get_random_data(byte**, int32*);
-
 enum {
 	// hashinit wants this many random bytes
 	HashRandomBytes = 32