contrib: fix gnutls build errors

This patch partially reverts GnuTLS commit 516f48bfbf33d111e4fcd310541baa8f160067ae, which prevents the daemon from building on some old Linux distributions due to increasing the minimum required version of autoconf from 2.64 to 2.71.

The patch also removes the AM_GNU_GETTEXT macros from the configure.ac file. When these macros are present, autoreconf calls autopoint, which overwrites some m4 files in the GnuTLS repository with the version found on the system. This causes the Ubuntu 20.04 and snap builds to fail with "possibly undefined macro" errors.

GitLab: #1111
Change-Id: I45b8225bff148b3cf01aa2ce14adc639de823a8f