Remove launch_powerkey_popup() and add signature for powerkey popup

Remove launch_powerkey_popup() and add signature for powerkey popup

There is no signature for powerkey popup, But actually, an array is made for dbus-send.

array [
   dict entry(
      string "_SYSPOPUP_CONTENT_"
      string "powerkey"
   )

The array is necessary in load_popup_by_type() for popup activation.
So, add signature a{ss} and use launch_popup() instead of launch_powerkey_popup()
for efficiency.

Change-Id: I4a95d5a8b1d054701d8b41ebb38658c6d1317bcc
Signed-off-by: lokilee73 <changjoo.lee@samsung.com>