Remove unnecessary delay in Arduino code.

Remove unnecessary delay in Arduino code.  This improves mean request
round-trip rate from ~50ms to ~12ms.

__NB__ Switching to the union protocol buffer type, described [here][1],
should help improve performance even farther by significantly reducing
message size in cases where there are many request types.  See 65cc525
for more details about the limitations of `nanopb` regarding union
types, and how to [work around the limitations][1].

[1]: https://code.google.com/p/nanopb/source/browse/examples/using_union_messages/README.txt