automation: remove Ubuntu 18.10

It reached end of life on July 18, 2019. I don't think we
should care about supporting it.

Differential Revision: https://phab.mercurial-scm.org/D6912

contrib/automation/hgautomation/aws.py

@@ -831,13 +831,6 b' def ensure_linux_dev_ami(c: AWSConnectio'
             'ubuntu/images/hvm-ssd/ubuntu-bionic-18.04-amd64-server-20190403',
         )
         ssh_username = 'ubuntu'
-    elif distro == 'ubuntu18.10':
-        image = find_image(
-            ec2resource,
-            UBUNTU_ACCOUNT_ID,
-            'ubuntu/images/hvm-ssd/ubuntu-cosmic-18.10-amd64-server-20190402',
-        )
-        ssh_username = 'ubuntu'
     elif distro == 'ubuntu19.04':
         image = find_image(
             ec2resource,

contrib/automation/hgautomation/linux.py

@@ -22,7 +22,6 b' from .ssh import ('
 DISTROS = {
     'debian9',
     'ubuntu18.04',
-    'ubuntu18.10',
     'ubuntu19.04',
 }