Remove duplicate check for merlin context (#175)

This check is done in add_rules and dot_merlin. Only of those checks is
necessary. The check in dot_merlin is removed.

src/merlin.ml

@@ -27,7 +27,6 @@ let ppx_flags sctx ~dir ~src_dir { preprocess; libname; _ } =
   | _ -> []
 
 let dot_merlin sctx ~dir ({ requires; flags; _ } as t) =
-  if (SC.context sctx).merlin then
   match Path.extract_build_context dir with
   | Some (_, remaindir) ->
     let path = Path.relative remaindir ".merlin" in