bootstrap: Remove last references to Ubuntu 16.04

The Ubuntu 16.04 build went away with
4366c3bb71 as oss-fuzz moves
to Ubuntu 20.04.

We don't do a special build for the oss-fuzz, this restores the
behaviour before e10910f8de and
d048d7e17d where oss-fuzz was only
tested as part of the main build.  (In the case of a failure the
pipeline would fail, preventing a merge, just the same as for
any other failing test).

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Uri Simchoni <uri@samba.org>

Autobuild-User(master): Uri Simchoni <uri@samba.org>
Autobuild-Date(master): Tue Sep 14 04:44:44 UTC 2021 on sn-devel-184

bootstrap/config.py

@@ -399,17 +399,6 @@ DEB_DISTS = {
             'liburing-dev': '',   # not available
         }
     },
-    'ubuntu1604': {
-        'docker_image': 'ubuntu:16.04',
-        'vagrant_box': 'ubuntu/xenial64',
-        'replace': {
-            'python3-gpg': 'python3-gpgme',
-            'glusterfs-common': '',
-            'libcephfs-dev': '',
-            'liburing-dev': '',   # not available
-            'libtracker-sparql-2.0-dev': '', # not available
-        }
-    },
     'ubuntu1804': {
         'docker_image': 'ubuntu:18.04',
         'vagrant_box': 'ubuntu/bionic64',