A pane's ID is immutable for the lifetime of the tmux server.
Same with window/session IDs.
When creating a new tmux repl, we record all three IDs to later use
them to send text to the repl.
The window/session IDs can be invalidating when a pane is moved to
a different window/session (via "tmux move-pane", "tmux move-window"
etc). This will cause repl-send-text to fail.
Fix this by dropping the redundant and potentially incorrect
window/session IDs. The immutable pane ID is enough.
37dcba9089