Could not load support for `gnome': libgnome.so: cannot open shared object file: No such file or directory

[Norbert]

Steps to reproduce:
1. Have Ubuntu 20.04 LTS installed
2. Install xscreensaver package
3. Launch `xscreensaver-demo`

Expected results:
* no warnings

Actual results:
* there are warnings:

```
$ xscreensaver-demo

(xscreensaver-demo:6824): libglade-WARNING **: 19:47:51.804: Could not load support for `gnome': libgnome.so: cannot open shared object file: No such file or directory
xscreensaver-demo: 19:47:52: XScreenSaver-debug: Name com.canonical.AppMenu.Registrar does not exist on the session bus

```

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: xscreensaver 5.42+dfsg1-1ubuntu1
ProcVersionSignature: Ubuntu 5.4.0-21.25-generic 5.4.27
Uname: Linux 5.4.0-21-generic x86_64
ApportVersion: 2.20.11-0ubuntu26
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: MATE
Date: Sun Apr 19 19:49:14 2020
InstallationDate: Installed on 2020-04-12 (6 days ago)
InstallationMedia: Ubuntu-MATE 20.04 LTS "Focal Fossa" - Beta amd64 (20200412)
SourcePackage: xscreensaver
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.