runtime: remove remaining use of MAKECONTEXT_STACK_TOP macro

    
    The definition and most uses of MAKECONTEXT_STACK_TOP were removed in
    https://golang.org/cl/88660043, which removed support for Solaris 8/9.
    One use of MAKECONTEXT_STACK_TOP was accidentally left in the source
    code.  Remove it now.
    
    Reviewed-on: https://go-review.googlesource.com/28911

From-SVN: r240045

gcc/go/gofrontend/MERGE

-4f033f29553655ad90493d55059a7bbc6cd63108
+b37a9e66ea584885043240f8f6f1d1c0284eadec
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/proc.c

@@ -2396,9 +2396,6 @@ __go_go(void (*fn)(void*), void* arg)
 		uc = ucontext_arg(&vnewg->context[0]);
 		getcontext(uc);
 		uc->uc_stack.ss_sp = vsp;
-#ifdef MAKECONTEXT_STACK_TOP
-		uc->uc_stack.ss_sp += vspsize;
-#endif
 		uc->uc_stack.ss_size = vspsize;
 		makecontext(uc, kickoff, 0);