Mark the NDK binder APIs as drafts.

These are still WIP and shouldn't be shipped in the NDK just yet.

Test: make checkbuild
Bug: None
Change-Id: Ifc4e935798edcd622bd34fb547d5177f5a084b32
diff --git a/libs/binder/ndk/Android.bp b/libs/binder/ndk/Android.bp
index 14ce4cb..91a5053 100644
--- a/libs/binder/ndk/Android.bp
+++ b/libs/binder/ndk/Android.bp
@@ -52,10 +52,12 @@
         "include_ndk/android/*.h",
     ],
     license: "NOTICE",
+    draft: true,
 }
 
 ndk_library {
     name: "libbinder_ndk",
     symbol_file: "libbinder_ndk.map.txt",
     first_version: "29",
+    draft: true,
 }