UI: Remove unused 'Percent' string

UI/data/locale/en-US.ini

@@ -93,7 +93,6 @@ Default="(Default)"
 Calculating="Calculating..."
 Fullscreen="Fullscreen"
 Windowed="Windowed"
-Percent="Percent"
 RefreshBrowser="Refresh"
 AspectRatio="Aspect Ratio <b>%1:%2</b>"
 LockVolume="Lock Volume"