build: drop the gitlog-to-changelog gnulib module

The use of this script was discontinued when we stopped providing a full
ChangeLog in the dist with:

  commit ce97c33a
  Author: Andrea Bolognani <abologna@redhat.com>
  Date:   Mon Apr 1 17:33:03 2019 +0200

    maint: Stop generating ChangeLog from git
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

Makefile.am

@@ -43,7 +43,6 @@ EXTRA_DIST = \
   AUTHORS.in \
   build-aux/augeas-gentest.pl \
   build-aux/check-spacing.pl \
-  build-aux/gitlog-to-changelog \
   build-aux/header-ifdef.pl \
   build-aux/minimize-po.pl \
   build-aux/mock-noinline.pl \

bootstrap.conf

@@ -54,7 +54,6 @@ getpass
 getpeername
 getsockname
 gettimeofday
-gitlog-to-changelog
 gnumakefile
 ignore-value
 intprops