flat only

remove option for uzers (users who are in reality fuzzers) to toggle flat option. The legacy arithmetic solver bakes in assumptions about flat format so it isn't helpful to expose this to fuzzers, I mean uzers.

src/ast/rewriter/th_rewriter.cpp

@@ -78,7 +78,7 @@ struct th_rewriter_cfg : public default_rewriter_cfg {
 
     void updt_local_params(params_ref const & _p) {
         rewriter_params p(_p);
-        m_flat           = p.flat();
+        m_flat           = true;
         m_max_memory     = megabytes_to_bytes(p.max_memory());
         m_max_steps      = p.max_steps();
         m_pull_cheap_ite = p.pull_cheap_ite();

src/params/rewriter_params.pyg

@@ -3,7 +3,6 @@ def_module_params('rewriter',
                   export=True,
                   params=(max_memory_param(),
                           max_steps_param(),
-                          ("flat", BOOL, True, "create nary applications for and,or,+,*,bvadd,bvmul,bvand,bvor,bvxor"),
                           ("push_ite_arith", BOOL, False, "push if-then-else over arithmetic terms."),
                           ("push_ite_bv", BOOL, False, "push if-then-else over bit-vector terms."),
                           ("pull_cheap_ite", BOOL, False, "pull if-then-else terms when cheap."),