Fix qps test.

This was failing to compile.
diff --git a/build.json b/build.json
index f0e8072..1e11b2a 100644
--- a/build.json
+++ b/build.json
@@ -1354,9 +1354,7 @@
       "build": "test",
       "c++": true,
       "src": [
-        "test/cpp/interop/empty.proto",
-        "test/cpp/interop/messages.proto",
-        "test/cpp/interop/test.proto",
+        "test/cpp/qps/qpstest.proto",
         "test/cpp/qps/client.cc"
       ],
       "deps": [
@@ -1373,9 +1371,7 @@
       "build": "test",
       "c++": true,
       "src": [
-        "test/cpp/interop/empty.proto",
-        "test/cpp/interop/messages.proto",
-        "test/cpp/interop/test.proto",
+        "test/cpp/qps/qpstest.proto",
         "test/cpp/qps/server.cc"
       ],
       "deps": [