pw_rpc: Enable echo_service_test in Bazel

Enable //pw_rpc/nanopb:echo_service_test in Bazel, since Nanopb options
files are supported.

Change-Id: Iae860e34a06e4301684be8a79d2243962bfc4105
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/247193
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
Docs-Not-Needed: Wyatt Hepler <hepler@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>

pw_rpc/nanopb/BUILD.bazel

@@ -277,14 +277,13 @@ pw_cc_test(
     ],
 )
 
-# TODO: b/234874064 - Requires nanopb options file support to compile.
-filegroup(
+pw_cc_test(
     name = "echo_service_test",
     srcs = ["echo_service_test.cc"],
-    #     deps = [
-    #       ":echo_service",
-    #       ":test_method_context",
-    #     ],
+    deps = [
+        ":echo_service",
+        ":test_method_context",
+    ],
 )
 
 pw_cc_test(