Remove unused Win32-specific bits.
Remove obsolete "experimental mode" option.

This was originally intended to activate the in-game UI (and thus
deactivate the native dialogs), but was never fleshed out.  In 2.0 there
are no more native dialogs, so this option is obsolete before it was
even used.
Remove old built-in profiler.

We may reimplement this in the future, but more likely we'll be making
use of the external profilers rather than a built-in one.