Revert "x11: Differentiate between mouse and keyboard focus #13943" (#13974)

This reverts #13943 and reopens #13897 since the fix in #13943 comes
with a regression:

Sometimes Zed loses keyboard focus and can't be restored. I haven't
figured out yet exactly when and how this happens and can't reliably
reproduce it yet, but there's something off with focus handling.

One reliable way to reproduce _one_ of the problems:

1. Open two zed windows
2. Focus one Zed window
3. Hover with the mouse over the other
4. Try to type in the window that should still be focused

So, to be careful, I'm going to revert the PR first, since I couldn't
find an obvious fix yet. If we do find a fix, we can unrevert.


Release Notes:

- N/A

crates/gpui/src/platform/linux/x11/window.rs

@@ -451,7 +451,6 @@ impl X11WindowState {
                         xinput::XIEventMask::MOTION
                             | xinput::XIEventMask::BUTTON_PRESS
                             | xinput::XIEventMask::BUTTON_RELEASE
-                            | xinput::XIEventMask::ENTER
                             | xinput::XIEventMask::LEAVE,
                     ],
                 }],