efl_gfx_color: fix color_code_set

efl_gfx_color: fix color_code_set

Summary:
There are two parts for this patch:
1- Fix sigmentation fault when using (efl_gfx_color_color_code_set).  // It try to modify const variable
2- Remove unnecessary code. // why would user pass slash or back slash as color code format.

Test Plan:
```
#define EFL_EO_API_SUPPORT 1
#define EFL_BETA_API_SUPPORT 1

#include <Eina.h>
#include <Elementary.h>
#include <Efl_Ui.h>

static void
_gui_quit_cb(void *data EINA_UNUSED, const Efl_Event *event EINA_UNUSED)
{
   efl_exit(0);
}

static void
_gui_setup()
{
   Eo *win, *rect;

   win = efl_add(EFL_UI_WIN_CLASS, efl_main_loop_get(),
                 efl_ui_win_type_set(efl_added, EFL_UI_WIN_TYPE_BASIC),
                 efl_text_set(efl_added, "Hello World"),
                 efl_ui_win_autodel_set(efl_added, EINA_TRUE));

   // when the user clicks "close" on a window there is a request to delete
   efl_event_callback_add(win, EFL_UI_WIN_EVENT_DELETE_REQUEST, _gui_quit_cb, NULL);
   rect = efl_add(EFL_CANVAS_RECTANGLE_CLASS,win);
   const char *color = "#FF0000FF";
   efl_gfx_color_code_set(rect,color);
   evas_object_resize(rect,250,250);
   evas_object_resize(win,250,250);
   evas_object_move(rect,0,0);
   evas_object_show(rect);
   evas_object_show(win);
}

EAPI_MAIN void
efl_main(void *data EINA_UNUSED, const Efl_Event *ev EINA_UNUSED)
{
   _gui_setup();
}
EFL_MAIN()
```

Reviewers: zmike, cedric, segfaultxavi, woohyun

Reviewed By: segfaultxavi

Subscribers: singh.amitesh, cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D9422