Remove the 10 second delay before user input generates engagement.
The site engagement service currently waits 10 seconds after
navigation completes before allowing user input to generate engagement.
This reduces the predictability of the service. Engagement also decays
much more quickly now, meaning that the additional engagement earned
when removing the 10 second wait is negligible.
This CL instead allows engagement to be earned from the moment that the
page finishes loading.