[egs] Fix issue #3662 in Chime example script (#3794)

Author: Peidong-Wang

egs/chime4/s5_1ch/local/rnnlm/tuning/run_lstm_1a.sh

@@ -66,6 +66,7 @@ if [ $stage -le 0 ]; then
   mkdir -p $text_dir
   cp $srcdir/train.rnn $text_dir/chime4.txt.tmp
   sed -e "s/<RNN_UNK>/<UNK>/g" $text_dir/chime4.txt.tmp > $text_dir/chime4.txt
+  rm $text_dir/chime4.txt.tmp
   cp $srcdir/valid.rnn $text_dir/dev.txt
 fi