Removed unused variable in merge headers unit test

`Headers1` is not used anywhere
diff --git a/src/couch_replicator/src/couch_replicator_httpc.erl b/src/couch_replicator/src/couch_replicator_httpc.erl
index 53158f9..cffeb86 100644
--- a/src/couch_replicator/src/couch_replicator_httpc.erl
+++ b/src/couch_replicator/src/couch_replicator_httpc.erl
@@ -507,7 +507,6 @@
 
 
 merge_headers_test() ->
-    Headers1 = [{"a", "x"}, {"a", "y"}, {"A", "z"}],
     ?assertEqual([], merge_headers([], [])),
     ?assertEqual([{"a", "x"}], merge_headers([], [{"a", "x"}])),
     ?assertEqual([{"a", "x"}], merge_headers([{"a", "x"}], [])),