Revert "Revert "Move error_code.h into otautil.""

This reverts commit 26436d6d6010d5323349af7e119ff8f34f85c40c to re-land
"Move error_code.h into otautil.".

This way it stops requiring relative path ".." in LOCAL_C_INCLUDES
(uncrypt and edify). Soong doesn't accept non-local ".." in
"local_include_dirs".

This CL needs to land with device-specific module changes (e.g. adding
the dependency on libotautil).

Test: lunch aosp_{angler,bullhead,dragon,fugu,sailfish}-userdebug;
      mmma bootable/recovery
Change-Id: If193241801af2dae73eccd31ce57cd2b81c9fd96
diff --git a/edify/expr.h b/edify/expr.h
index 3282802..770d1cf 100644
--- a/edify/expr.h
+++ b/edify/expr.h
@@ -23,7 +23,7 @@
 #include <string>
 #include <vector>
 
-// Forward declaration to avoid including "error_code.h".
+// Forward declaration to avoid including "otautil/error_code.h".
 enum ErrorCode : int;
 enum CauseCode : int;