Efl.Ui.Button_Legacy: Prevent duplicate signal emit of contents

Efl.Ui.Button_Legacy: Prevent duplicate signal emit of contents

Summary:
When call elm_button_add, theme_apply of layout is called and
_efl_ui_button_legacy_efl_ui_widget_theme_apply is called.
Then it calls the signal emit for the icon.
In the button theme, the default of the icon is hidden,
so this call is unnecessary.

Test Plan:
Evas_Object *bt;
clock_t start, finish;
start = clock();
bt = elm_button_add(win);
finish = clock();
printf("duration : %f\n", (double)(finish-start)/CLOCKS_PER_SEC);

Evas_Object *bt;
clock_t start, finish;
double sum= 0 ;
double avg = 0;
double cnt = 1000;

for(int i =0 ; i<(int)cnt; i++)
  {
     start = clock();
     bt = elm_button_add(win);
     finish = clock();
     sum += (double)(finish-start)/CLOCKS_PER_SEC;
  }
avg = sum / cnt ;
printf("button avg : %f %f\n",avg, sum);

[before]
button avg : 0.000215

[after]
button avg : 0.000138

Reviewers: Hermet, YOhoho, Jaehyun_Cho, zmike

Reviewed By: zmike

Subscribers: zmike, cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D11810