Revert "preprocess ocaml sources via sedlex.ppx (#6926)"

This reverts commit 5f817aae9f5fed2a4f05d5a6fc966583d102ddcc.

Makefile

@@ -61,9 +61,7 @@ else
 	OCAMLDEP_FLAGS = -native
 endif
 
-PPX_SEDLEX = $(shell ocamlfind printppx sedlex.ppx)
-
-CC_CMD = ($(COMPILER) $(PPX_SEDLEX) $(ALL_CFLAGS) -c $< 2>tmp.tmp && $(MESSAGE_FILTER)) || ($(MESSAGE_FILTER) && exit 1)
+CC_CMD = ($(COMPILER) $(ALL_CFLAGS) -c $< 2>tmp.tmp && $(MESSAGE_FILTER)) || ($(MESSAGE_FILTER) && exit 1)
 
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