disable gazebo classic as focal is EOL

Signed-off-by: Mikael Arguedas <[email protected]>

library/gazebo

@@ -1,19 +1,2 @@
 Maintainers: Tully Foote <[email protected]> (@tfoote)
 GitRepo: https://github.com/osrf/docker_images.git
-
-################################################################################
-# Release: 11
-
-########################################
-# Distro: ubuntu:focal
-
-Tags: gzserver11, gzserver11-focal
-Architectures: amd64
-GitCommit: f7bb3258d4814deec1eca7e46cbb8d7f4b054431
-Directory: gazebo/11/ubuntu/focal/gzserver11
-
-Tags: libgazebo11, libgazebo11-focal, latest
-Architectures: amd64
-GitCommit: f7bb3258d4814deec1eca7e46cbb8d7f4b054431
-Directory: gazebo/11/ubuntu/focal/libgazebo11
-