x11: remove unused stuff

Unfortunately, it looks like some Motif functionality is still needed
to allow for --no-border.
x11: remove a MWM hack

This was for Motif Window Manager. No, I don't care about Motif.
x11: replace--[x11-]fstype option with --x11-netwm

Simplifies the code a lot. You can still use --x11-netwm=no to disable
NetWM for whatever reasons.