[Fuchsia] use default packet count in FuchsiaVideoDecoder.

The packet_count_for_client_min is 1 in this case.  The default is
3 (so far).  The default of 3 works fine, but 0 is below min.  The min
will be enforced soon so this CL prepares for that.

Change-Id: Ia1184156d0aa4945f39dab2b69bea0d64ebab854
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574680
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Dustin Green <dustingreen@google.com>
Cr-Commit-Position: refs/heads/master@{#652312}