Drop ubuntu-18.04 from acceptance and esbake builds

Stops building server packages for eol'd ubuntu-18.04, and drops it from
the default os for acceptance testing. In particular, openvoxdb is
difficult to test on ubuntu-18.04 due to lack of unarchived postgres
packages.

Author: jpartlow

.github/workflows/beaker_acceptance.yml

@@ -198,7 +198,6 @@ on:
             ["debian", "12"],
             ["rocky", "8"],
             ["rocky", "9"],
-            ["ubuntu", "18.04"],
             ["ubuntu", "20.04"],
             ["ubuntu", "22.04"],
             ["ubuntu", "24.04"]

.github/workflows/build_ezbake.yml

@@ -29,7 +29,7 @@ env:
   # https://github.com/boto/boto3/issues/4398#issuecomment-2619946229
   AWS_REQUEST_CHECKSUM_CALCULATION: "WHEN_REQUIRED"
   AWS_RESPONSE_CHECKSUM_VALIDATION: "WHEN_REQUIRED"
-  DEB_PLATFORMS: ${{ inputs.deb_platform_list || 'ubuntu-18.04,ubuntu-20.04,ubuntu-22.04,ubuntu-24.04,debian-11,debian-12' }}
+  DEB_PLATFORMS: ${{ inputs.deb_platform_list || 'ubuntu-20.04,ubuntu-22.04,ubuntu-24.04,debian-11,debian-12' }}
   RPM_PLATFORMS: ${{ inputs.rpm_platform_list || 'el-7,el-8,el-9,el-10,sles-15,amazon-2023' }}
   EZBAKE_BRANCH: ${{ inputs.ezbake-ref }}