[Fuchsia] Don't include internal syscalls header

The <zircon/syscalls/definitions.h> header is an implementation detail
of the OS that was never meant to be used by application code.
<zircon/syscalls.h> alone gives access to the Zircon syscall API.

Bug: fuchsia:45844
Change-Id: I0a1594e36c5eb6a05ff2266461970e49958c34bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2055591
Auto-Submit: Roland McGrath <mcgrathr@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741543}

base/debug/stack_trace_fuchsia.cc

@@ -11,7 +11,6 @@
 #include <unwind.h>
 #include <zircon/process.h>
 #include <zircon/syscalls.h>
-#include <zircon/syscalls/definitions.h>
 #include <zircon/syscalls/port.h>
 #include <zircon/types.h>