core/events: fix cursor tracking for other backends
The cursor rendering code path used by the screen cast code relies on the cursor tracker machinery to determine where to blit the cursor texture, but at the moment the cursor position invalidation is behind a check for whether the shell is using a Wayland backend. (This code path used to be Wayland-specific before 00cbcb7b but has been backend-agnostic since).
This commit removes the check for a Wayland compositor, allowing cursor drawing to function correctly on X11 when screen casting in embedded cursor mode. Fixes #1780 (closed).