javadoc: exclude internal APIs

Fixes #5858 in master
diff --git a/api/build.gradle b/api/build.gradle
index 98a4d5b..7c399d2 100644
--- a/api/build.gradle
+++ b/api/build.gradle
@@ -28,5 +28,4 @@
 javadoc {
     // We want io.grpc.Internal, but not io.grpc.Internal*
     exclude 'io/grpc/Internal?*.java'
-    exclude 'io/grpc/internal/**'
 }
diff --git a/core/build.gradle b/core/build.gradle
index c822177..f57c084 100644
--- a/core/build.gradle
+++ b/core/build.gradle
@@ -32,6 +32,7 @@
 }
 
 javadoc {
+    exclude 'io/grpc/internal/**'
     // Disabled until kinda stable.
     exclude 'io/grpc/perfmark/**'
 }