delete more default constructors

reduces code size by 0.1%

src/ast/converters/model_converter.h

@@ -71,9 +71,6 @@ protected:
     void display_del(std::ostream& out, func_decl* f) const;
     void display_add(std::ostream& out, ast_manager& m);
 public:
-
-    model_converter() {}
-
     void set_completion(bool f) { m_completion = f; }
 
     virtual void operator()(model_ref & m) = 0;

src/ast/recfun_decl_plugin.cpp

@@ -417,7 +417,6 @@ namespace recfun {
     }
 
     namespace decl {
-        plugin::plugin() : decl_plugin(), m_defs(), m_case_defs() {}
         plugin::~plugin() { finalize(); }
 
         void plugin::finalize() {

src/ast/recfun_decl_plugin.h

@@ -173,7 +173,6 @@ namespace recfun {
             void compute_scores(expr* e, obj_map<expr, unsigned>& scores);
 
         public:
-            plugin();
             ~plugin() override;
             void finalize() override;
 

src/ast/rewriter/var_subst.h

@@ -94,7 +94,7 @@ class expr_free_vars {
     ptr_vector<sort> m_sorts;
     ptr_vector<expr> m_todo;
 public:
-    expr_free_vars() {}
+    expr_free_vars() = default;
     expr_free_vars(expr* e) { (*this)(e); }
     void reset();
     void operator()(expr* e);

src/ast/simplifiers/linear_equation.h

@@ -35,7 +35,7 @@ private:
     mpz *      m_as;        // precise coefficients
     double *   m_approx_as; // approximated coefficients
     var *      m_xs;        // var ids
-    linear_equation() {}
+    linear_equation() = default;
 public:
     unsigned size() const { return m_size; }
     mpz const & a(unsigned idx) const { SASSERT(idx < m_size); return m_as[idx]; }