How to quit "Force Quit Applications" using AppleScript?
You can use this Apple Script to close this window:

tell application "System Events"
    key code 53 using {command down, option down} -- ESC + ALT + CMD
    keystroke "w" using command down
end tell


This window is owned by loginwindow process and it's not that easy to interact with it. Here's the code to press Force Quit button on this window:

tell application "System Events" to tell process "loginwindow"
    click button 1 of window 1 
end tell


However this does not work:

tell application "System Events" to tell process "loginwindow"
    close window 1
end tell