Revert "CI: Revert from UEFI to BIOS mode in TLS jobs"

This reverts commit b2e8e715.

Reason for revert: Other measures were taken to reduce memory overhead.

Change-Id: I4987480b4ed1bd4bd95a0ae72861f471cc229e20

zuul.d/jobs.yaml

@@ -122,6 +122,7 @@
     parent: kayobe-overcloud-base
     vars:
       tls_enabled: true
+      ironic_boot_mode: "uefi"
 
 - job:
     name: kayobe-overcloud-tls-centos8s