Remove CHROMIUM_ROLLING_MAGENTA_TO_ZIRCON scaffolding.

https://chromium-review.googlesource.com/c/chromium/src/+/669139 has
landed.

Bug: chromium:765754
Change-Id: I6f6c52f053698348673eaa1e2574801b3f6b2041
Reviewed-on: https://boringssl-review.googlesource.com/20505
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

crypto/rand_extra/fuchsia.c

@@ -19,16 +19,7 @@
 #include <limits.h>
 #include <stdlib.h>
 
-// TODO(davidben): Remove this once https://crbug.com/765754 is resolved.
-#if defined(CHROMIUM_ROLLING_MAGENTA_TO_ZIRCON)
 #include <zircon/syscalls.h>
-#else
-#include <magenta/syscalls.h>
-#define ZX_CPRNG_DRAW_MAX_LEN MX_CPRNG_DRAW_MAX_LEN
-#define ZX_OK MX_OK
-#define zx_status_t mx_status_t
-#define zx_cprng_draw mx_cprng_draw
-#endif
 
 #include "../fipsmodule/rand/internal.h"