Also get rid of TMP_FILE in todo.cfg.

There's a slight chance that some add-on has used this (undocumented, unofficial) configuration value for its own purposes (and maybe also relied on the unexposed cleanup() infrastructure), but detecting and fixing that problem (by moving the cleanup into the add-on itself) is pretty straightforward.

todo.cfg

@@ -8,7 +8,6 @@ export TODO_DIR=`dirname "$0"`
 export TODO_FILE="$TODO_DIR/todo.txt"
 export DONE_FILE="$TODO_DIR/done.txt"
 export REPORT_FILE="$TODO_DIR/report.txt"
-export TMP_FILE="$TODO_DIR/todo.tmp"
 
 # You can customize your actions directory location
 #export TODO_ACTIONS_DIR="$HOME/.todo.actions.d"