The following GUI script seems to do what you are asking for, at least with Keynote 6.6.2 under OS X 10.11.3:
tell application "Keynote"
activate
set N1 to count the slides of document 1
end tell
tell application "System Events" to clickmenu item "First Slide" of menu 1 of menu item "Go To" of menu 1 of menu bar item "Slide" of menu bar 1 of process "Keynote"
repeat N1 times
tell application "Keynote" to set N2 to countiWork items of current slide of document 1
tell application "System Events"
repeat N2 times
keystroketab
clickmenu item "Use None" of menu 1 of menu item "Ligature" of menu 1 of menu item "Font" of menu 1 of menu bar item "Format" of menu bar 1 of process "Keynote"
end repeat
clickmenu item "Next Slide" of menu 1 of menu item "Go To" of menu 1 of menu bar item "Slide" of menu bar 1 of process "Keynote"
end tell
end repeat
tell application "System Events" to clickmenu item "First Slide" of menu 1 of menu item "Go To" of menu 1 of menu bar item "Slide" of menu bar 1 of process "Keynote"
Also have a look at this article.