remove '#include <iostream>' from headers and from unneeded places

It's harmful to have iostream everywhere as it injects functions in the compiled files

src/parsers/smt2/marshal.h

@@ -12,7 +12,7 @@ Abstract:
 #pragma once
 
 #include <string>
-#include <iostream>
+#include <ostream>
 
 #include "ast/ast.h"
 

src/parsers/smt2/smt2scanner.h

@@ -18,7 +18,7 @@ Revision History:
 --*/
 #pragma once
 
-#include<iostream>
+#include<istream>
 #include "util/symbol.h"
 #include "util/vector.h"
 #include "util/rational.h"

src/parsers/util/cost_parser.h

@@ -26,7 +26,6 @@ class cost_parser : public simple_parser {
     var_ref_vector m_vars;
 public:
     cost_parser(ast_manager & m);
-    ~cost_parser() override {}
     expr * parse_int(rational const & r) override;
     expr * parse_float(rational const & r) override;
     unsigned add_var(symbol name);

src/parsers/util/scanner.cpp

@@ -17,6 +17,7 @@ Revision History:
 
 --*/
 #include "parsers/util/scanner.h"
+#include <iostream>
 
 inline int scanner::read_char() {
     if (m_is_interactive) {

src/parsers/util/simple_parser.cpp

@@ -17,6 +17,7 @@ Revision History:
 
 --*/
 #include<fstream>
+#include<iostream>
 #include<sstream>
 #include "parsers/util/simple_parser.h"
 #include "util/warning.h"