Remove unnecessary fold_convert in gfc_(un)likely

Remove unnecessary fold_convert in gfc_(un)likely

This patch removes an unnecessary fold_convert to boolean_type_node at
the end of gfc_likely and gfc_unlikely.  It makes no difference to the
generated code, but makes tree dumps a little bit cleaner.

2017-09-25  Janne Blomqvist  <jb@gcc.gnu.org>
        * trans.c (gfc_unlikely): Remove unnecessary fold_convert.
        (gfc_likely): Likewise.

Regtested on x86_64-pc-linux-gnu.

From-SVN: r253132