X11Utils: Remove unneeded SendButtonEvent / SendKeyEvent utilities

This was used to send fake button or key events to every backend to
implement freelook. When I ported these to be based on wx events in
commit 5248211, I didn't realize that these were now unused, so I didn't
remove them. Do that now.
Merge pull request #752 from magcius/remove-bootleg-events

X11Utils: Remove unneeded SendButtonEvent / SendKeyEvent utilities