e-sink.el: remove unrelated statement from when-form
e-sink.el: collapse multiple let-forms into one
e-sink.el: fix minor typo
e-sink.pl: remove --cmd

The --cmd command-line switch attempts to get e-sink to send strings
over the command-line, as opposed to using a temporary file.  Apart
from being horribly ugly, it always fails with:

  Argument list too long at /usr/bin/e-sink.pl line 47, <STDIN> line
  53857.

So, remove this command-line switch altogether.  While at it, also
remove the corresponding function e-sink-receive() in e-sink.el.
e-sink.pl: implement perlcritic --gentle suggestions

Don't use subroutine prototypes, and use the three-argument form of
open().