move to libcurl4-gnutls

Why: Debian trixie does not build
make deb
dpkg-checkbuilddeps: error: Unmet build dependencies: libcurl4-nss-dev

Debian trixie removed libcurl4-nss-dev while sid still has it.
And #1202  sugests to move to libcur4-gnutls

Signed-off-by: Antony Antony <antony@phenome.org>

packaging/debian/control

@@ -16,7 +16,7 @@ Build-Depends:
  htmldoc,
  libaudit-dev [linux-any],
  libcap-ng-dev [linux-any],
- libcurl4-nss-dev,
+ libcurl4-gnutls-dev,
  libevent-dev,
  libkrb5-dev,
  libldap2-dev,