Obsolete BUILD_BROKEN_DUP_COPY_HEADERS

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Test: treehugger
Change-Id: I1fd5b933372e3ea391c121d265f41c35b832b206
diff --git a/core/Makefile b/core/Makefile
index 7fa7a6b..6602a29 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -91,9 +91,7 @@
 
 ifdef has_dup_copy_headers
   has_dup_copy_headers :=
-  ifneq ($(BUILD_BROKEN_DUP_COPY_HEADERS),true)
-    $(error duplicate header copies are no longer allowed. For more information about headers, see: https://android.googlesource.com/platform/build/soong/+/master/docs/best_practices.md#headers)
-  endif
+  $(error duplicate header copies are no longer allowed. For more information about headers, see: https://android.googlesource.com/platform/build/soong/+/master/docs/best_practices.md#headers)
 endif
 
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