run_undoable_changes now called from insdel.

run_undoable_changes now called from insdel.

The original calls from inside undo.c are not always at a safe position
to call lisp, as they originate in varied positions within insdel.c.
Calling them directly from prepare_to_modify_buffer_1 ensures that they
are always run at the same point.

 * undo.c (run_undoable_changes,syms_of_undo): Remove function
 and symbol used.
 * insdel.c (run_undoable_changes): Add function and symbol.