pw_rpc: Rename ServerCall to CallContext

The ServerCall object will be used for both the server and client, so
rename it to "CallContext".

Change-Id: I360f923e1d322ff4c8ee3876e7c51fcfcf6f6dc3
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/59486
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
diff --git a/pw_rpc/service_test.cc b/pw_rpc/service_test.cc
index 959323f..fb27848 100644
--- a/pw_rpc/service_test.cc
+++ b/pw_rpc/service_test.cc
@@ -29,7 +29,7 @@
 namespace {
 
 void InvokeIt(const internal::Method&,
-              internal::ServerCall&,
+              internal::CallContext&,
               const internal::Packet&) {}
 
 class ServiceTestMethod : public internal::Method {