Revert "SE-0157: Enable recursive protocol constraints by default."

This reverts commit afbdbae9d9.

Commit ded45a6e1c more than triples the
type checking time when building Swift.o, so I am going to revert that ,
and it looks like this needs to be reverted as well if that commit is
reverted.

lib/Frontend/CompilerInvocation.cpp

@@ -1007,6 +1007,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
   }
   
   Opts.EnableASTScopeLookup |= Args.hasArg(OPT_enable_astscope_lookup);
+  Opts.EnableRecursiveConstraints |=
+    Args.hasArg(OPT_enable_recursive_constraints);
   Opts.DebugConstraintSolver |= Args.hasArg(OPT_debug_constraints);
   Opts.EnableConstraintPropagation |= Args.hasArg(OPT_propagate_constraints);
   Opts.IterativeTypeChecker |= Args.hasArg(OPT_iterative_type_checker);