s/IMPL_HEADER/IMPL_INTERFACE/g

More appropriate name for this enum constant now that they are defined
in the interface source files.

Test: hidl_test
Change-Id: Ice531adb797c3213a2da18421b7e97fcfc888da3
diff --git a/Method.cpp b/Method.cpp
index 9d40856..c967d89 100644
--- a/Method.cpp
+++ b/Method.cpp
@@ -47,7 +47,7 @@
     mJavaImpl = javaImpl;
 
     CHECK(mJavaImpl.find(IMPL_STUB_IMPL) == mJavaImpl.end())
-            << "FATAL: mJavaImpl should not use IMPL_STUB_IMPL; use IMPL_HEADER instead.";
+            << "FATAL: mJavaImpl should not use IMPL_STUB_IMPL; use IMPL_INTERFACE instead.";
     CHECK(mCppImpl.find(IMPL_STUB_IMPL) == mCppImpl.end() ||
           mCppImpl.find(IMPL_STUB) == mCppImpl.end())
             << "FATAL: mCppImpl IMPL_STUB will override IMPL_STUB_IMPL.";