pw_rpc: Reorganize Nanopb implementation

As with raw, replace "nanopb_" file prefixes with a directory path.

Change-Id: Id7e21069850fbfe61bcc3d644881d5f0411830e6
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/52863
Commit-Queue: Wyatt Hepler <hepler@google.com>
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
diff --git a/pw_rpc/nanopb/CMakeLists.txt b/pw_rpc/nanopb/CMakeLists.txt
index 66547f9..6f879f7 100644
--- a/pw_rpc/nanopb/CMakeLists.txt
+++ b/pw_rpc/nanopb/CMakeLists.txt
@@ -16,7 +16,7 @@
 
 pw_add_module_library(pw_rpc.nanopb.method
   SOURCES
-    nanopb_method.cc
+    method.cc
   PUBLIC_DEPS
     pw_rpc.nanopb.common
     pw_rpc.server
@@ -35,7 +35,7 @@
 
 pw_add_module_library(pw_rpc.nanopb.client
   SOURCES
-    nanopb_client_call.cc
+    client_call.cc
   PUBLIC_DEPS
     pw_function
     pw_rpc.nanopb.common
@@ -44,7 +44,7 @@
 
 pw_add_module_library(pw_rpc.nanopb.common
   SOURCES
-    nanopb_common.cc
+    common.cc
   PUBLIC_DEPS
     pw_bytes
     pw_rpc.common