move input_line from command_line to simplewallet

It was only used there, and this removes one part of the common
dependency on libreadline

src/common/command_line.cpp

@@ -36,10 +36,6 @@
 #include "cryptonote_config.h"
 #include "string_tools.h"
 
-#ifdef HAVE_READLINE
-  #include "readline_buffer.h"
-#endif
-
 namespace command_line
 {
   namespace
@@ -50,20 +46,6 @@ namespace command_line
     }
   }
 
-  std::string input_line(const std::string& prompt)
-  {
-#ifdef HAVE_READLINE
-    rdln::suspend_readline pause_readline;
-#endif
-    std::cout << prompt;
-
-    std::string buf;
-    std::getline(std::cin, buf);
-
-    return epee::string_tools::trim(buf);
-
-  }
-
   bool is_yes(const std::string& str)
   {
     if (str == "y" || str == "Y")