pw_rpc: Remove #includes from nanopb codegen
pw_rpc: Remove #includes from nanopb codegen

This change updates the RPC codegen to not #include imported proto
files, as those are already included from the corresponding nanopb
header.

Change-Id: Id2bd7db4c68ea909b7c0722a65196a304ecf8378
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/14440
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Commit-Queue: Alexei Frolov <a1b001416a8cf9aaea32a3411f8f3c0793ebc0b5@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed