Clean-up gmx_eof

- Changed name to gmx_one_before_eof so that the different
  behavior from feof is obvious.
- Changed one usage of gmx_eof to feof where the std
  behavior is OK
- Moved to confio and made static because it is only
  used there.
- Removed the special treatment for pipes. It was incorrect.
  gmx_before_eof is only used for gro file reading and
  those could not be read from compressed files anyhow.
  Their is no possible correct implemenation for pipes
  (which cannot be seeked) and even if it wouldn't help
  because gro file reading also uses rewind which
  doesn't work for pipes.

Change-Id: I77fd34253817cd591011b8a2ec39ae95ce7b7378