Pax requested the keyboard shortcut be removed — too easy to fat-finger
when navigating with the keyboard, and "Open in Default App" still
ships an external process that may steal focus from the app. The
right-click menu's Open in Default App action stays, both on browse
thumbnails and in the preview pane right-click — only the bare-key
shortcut goes away.
The deleted block was the only Key_O handler in BooruApp.keyPressEvent,
so no other behavior changes.
Verified manually:
- press O on a selected thumbnail → nothing happens
- right-click thumbnail → "Open in Default App" still present and opens
- right-click preview pane → same