libbinder_ndk: C++ headers aren't C-compatible.

These were allowed to be included in C code, but weren't useful.

Bug: 111445392
Test: atest android.binder.cts
Change-Id: Ib26d784076ed99c4270e2bdb10480aaf472ef01e
diff --git a/libs/binder/ndk/include_ndk/android/binder_auto_utils.h b/libs/binder/ndk/include_ndk/android/binder_auto_utils.h
index cdae6bb..5c26039 100644
--- a/libs/binder/ndk/include_ndk/android/binder_auto_utils.h
+++ b/libs/binder/ndk/include_ndk/android/binder_auto_utils.h
@@ -31,10 +31,8 @@
 #include <android/binder_status.h>
 
 #include <assert.h>
+
 #include <unistd.h>
-
-#ifdef __cplusplus
-
 #include <cstddef>
 
 namespace ndk {
@@ -252,6 +250,4 @@
 
 }  // namespace ndk
 
-#endif  // __cplusplus
-
 /** @} */