Refactored all of the desugaring code to no longer depend on memory being initialized to 0. Everything is about 12% faster now.

src/parsers/butnot.c

@@ -35,16 +35,10 @@ static HParseResult* parse_butnot(void *env, HParseState *state) {
   }
 }
 
-static HCFChoice* desugar_butnot(HAllocator *mm__, void *env) {
-  assert_message(0, "'h_butnot' is not context-free, can't be desugared");
-  return NULL;
-}
-
 static const HParserVtable butnot_vt = {
   .parse = parse_butnot,
   .isValidRegular = h_false,
   .isValidCF = h_false, // XXX should this be true if both p1 and p2 are CF?
-  .desugar = desugar_butnot,
   .compile_to_rvm = h_not_regular,
 };