[fuchsia] Finish migration to fdio_pipe_half

fdio_pipe_half is now the same as fdio_pipe_half2. We can complete the
migration by switch back to the cleaner name.

Change-Id: I6fbec450b9e2e1a4be1e68b8f9281e4d3e370e07
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/104805
Auto-Submit: Adam Barth <abarth@google.com>
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Zach Anderson <zra@google.com>

runtime/bin/process_fuchsia.cc

@@ -678,7 +678,7 @@ class ProcessStarter {
 
   zx_status_t AddPipe(int target_fd, int* local_fd,
                       fdio_spawn_action_t* action) {
-    zx_status_t status = fdio_pipe_half2(local_fd, &action->h.handle);
+    zx_status_t status = fdio_pipe_half(local_fd, &action->h.handle);
     if (status != ZX_OK) return status;
     action->action = FDIO_SPAWN_ACTION_ADD_HANDLE;
     action->h.id = PA_HND(PA_HND_TYPE(PA_FD), target_fd);