gh-75666: Tkinter: "unbind(sequence, funcid)" now only unbinds "funcid" (GH-111322)

gh-75666: Tkinter: "unbind(sequence, funcid)" now only unbinds "funcid" (GH-111322)

Previously, "widget.unbind(sequence, funcid)" destroyed the current binding
for "sequence", leaving "sequence" unbound, and deleted the "funcid"
command.

Now it removes only "funcid" from the binding for "sequence", keeping
other commands, and deletes the "funcid" command.
It leaves "sequence" unbound only if "funcid" was the last bound command.

Co-authored-by: GiovanniL <13402461+GiovaLomba@users.noreply.github.com>