Remove the sprite cursor path once the native cursor has proven itself #372

Since #369 transform sessions use the native cursor (DWM-drawn pointer via the cursor lens) by default. The old path (CursorSprite, twin band windows, CursorBlanker swaps at zoom-in/out, the shell-panel pointer freeze, wobble cage) only runs with txNativeCursor=0.

Once the native cursor has been in daily use for a while without regressions, remove the sprite path and its settings to shrink the cursor system. Keep: Inspect's crosshair (it still uses the sprite window) and the blanker for Inspect and the hide-cursor hotkey, or move those onto a smaller helper.