Require Libgpg-error 1.27

* configure.ac (NEED_GPG_ERROR_VERSION): Require 1.27
* common/util.h: Remove compatibility macros.

This is just a minor change to align with the need for Libgcrypt 1.8.
The latter was first released in summer 2017 while Libgpg-error 1.27
was released earlier in spring that year.

• Signed-off-by: Werner Koch <wk@gnupg.org>