ERASE_LINE
  Erases the current line from the current buffer; optionally returns a
  string representing the erased line for use in other DECTPU procedures.
  Syntax
     [string] := ERASE_LINE
  Example
     take_out_line := ERASE_LINE;
  Erases the current line in the current buffer and stores in the variable
  TAKE_OUT_LINE the string of characters representing the erased line.
  Related topics
     COPY_TEXT   DELETE   ERASE   ERASE_CHARACTER