Replace find_temporary_table() with is_temporary_table()

DROP TABLE opens all temporary tables at start, but then
uses find_temporary_table() to check if a table is temporary
instead of is_temporary_table() which is much faster.

This patch fixes this issue.

sql/sql_parse.cc

@@ -4930,7 +4930,7 @@ mysql_execute_command(THD *thd)
       {
         if (!lex->tmp_table() &&
            (!thd->is_current_stmt_binlog_format_row() ||
-	    !thd->find_temporary_table(table)))
+	    !is_temporary_table(table)))
         {
           WSREP_TO_ISOLATION_BEGIN(NULL, NULL, all_tables);
           break;

sql/sql_table.cc

@@ -2131,8 +2131,7 @@ bool mysql_rm_table(THD *thd,TABLE_LIST *tables, bool if_exists,
     {
       LEX_CSTRING db_name= table->db;
       LEX_CSTRING table_name= table->table_name;
-      if (table->open_type == OT_BASE_ONLY ||
-          !thd->find_temporary_table(table))
+      if (!is_temporary_table(table))
         (void) delete_statistics_for_table(thd, &db_name, &table_name);
     }
   }