Remove unused helper function from ffplay.go

The `PrepareBackgroundCommand` function has been removed because it prevents the program window from being displayed on Windows.

kernel/ffplay.go

@@ -1,7 +1,6 @@
 package kernel
 
 import (
-	"git.kor-elf.net/kor-elf/gui-for-ffmpeg/helper"
 	"os/exec"
 )
 
@@ -24,7 +23,6 @@ func NewFFplay(ffPathUtilities *FFPathUtilities) *FFplay {
 func (ffplay FFplay) Run(setting FFplaySetting) error {
 	args := []string{setting.PathToFile}
 	cmd := exec.Command(ffplay.ffPathUtilities.FFplay, args...)
-	helper.PrepareBackgroundCommand(cmd)
 
 	return cmd.Start()
 }