Remove check for whether AM_GNU_GETTEXT_VERSION is defined; assume it always is.
This works around this erroneous complaint from gettext 1.0's autopoint:

autopoint: *** found more than one invocation of AM_GNU_GETTEXT_VERSION
autopoint: *** Stop.

https://gitlab.com/rockdaboot/libhsts/-/work_items/6
--- configure.ac.orig	2026-06-21 16:11:30.000000000 -0500
+++ configure.ac	2026-06-21 16:13:57.000000000 -0500
@@ -34,10 +34,7 @@
 m4_ifdef([AM_GNU_GETTEXT], [
   AM_GNU_GETTEXT([external],[need-ngettext])
 ])
-m4_ifdef([AM_GNU_GETTEXT_VERSION], [
-#do not indent here
 AM_GNU_GETTEXT_VERSION([0.18.2])
-])
 
 #
 # check for doxygen and pandoc