Use returnFalse instead of jQuery.noop

Follows-up 86622b6.

While these functions looked like placeholders in a configuration
object to allow calling them unconditionally, they actually had
meaning. They were event overrides to prevent WikiEditor from
running its own event handlers.

They were implicitly returning false by having no return statement
(implying a 'return undefined', which casts to false).

The separate functions were already quite obfuscated as returning
false, using $.noop made it even harder to understand what's
going on.

Use an explicit return value instead.

Change-Id: I0852fbc9225d069f50085787d2d0105fd7b1743c