[ocamlformat] Exclude deadcode/dune.in from list of ocaml dune files

Summary:
infer/src/deadcode/dune.in is not an OCaml-syntax dune file, so
exclude it from the list computed for use by the auto-formatter.

Reviewed By: jvillard

Differential Revision: D21583047

fbshipit-source-id: 13a99a89b

Makefile

@@ -221,7 +221,7 @@ fb-setup:
 fmt:
 	parallel $(OCAMLFORMAT_EXE) $(OCAMLFORMAT_ARGS) -i ::: $$(git diff --name-only --diff-filter=ACMRU $$(git merge-base origin/master HEAD) | grep "\.mli\?$$")
 
-DUNE_ML:=$(shell find * -name 'dune*.in' | grep -v workspace | grep -v infer-source)
+DUNE_ML:=$(shell find * -name 'dune*.in' | grep -v workspace | grep -v infer-source | grep -v infer/src/deadcode/dune.in)
 
 .PHONY: fmt_dune
 fmt_dune: