USN-8944-2: ca-certificates update

USN-8944-1 updated ca-certificates. This update provides the corresponding changes for Ubuntu 14.04 LTS, Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS by removing the "emSign ECC Root CA - G3" and "Comodo AAA Services root" CA certificates. Original advisory details: This update removes the "emSign ECC Root CA - G3" CA certificate due to intermediate CA certificates being compromised.