Use only Yoga tests

TC has decided to keep support for Python 3.6 during the Yoga cycle.
For more info see [1]

[1] http://lists.openstack.org/pipermail/openstack-discuss/2021-December/026164.html

Change-Id: Icfe518fafa2b012e034a2e8ff18c242843df0086

zuul.d/project.yaml

@@ -8,11 +8,6 @@
       - release-notes-jobs-python3
     check:
       jobs:
-        # NOTE(rpittau): yoga jobs support py38 and py39 but we want to keep
-        # testing py36 to maintain compatibility with older distributions like
-        # CentOS Stream 8, Ubuntu Bionic, Debian 10, and openSuse Leap
-        # Remove after Yoga
-        - openstack-tox-py36
         - openstack-tox-functional
         - ipa-tox-examples
         # NOTE(iurygregory) Only run this two jobs since we are testing
@@ -41,11 +36,6 @@
     gate:
       queue: ironic
       jobs:
-        # NOTE(rpittau): yoga jobs support py38 and py39 but we want to keep
-        # testing py36 to maintain compatibility with older distributions like
-        # CentOS Stream 8, Ubuntu Bionic, Debian 10, and openSuse Leap
-        # Remove after Yoga
-        - openstack-tox-py36
         - openstack-tox-functional
         - ipa-tempest-bios-ipmi-direct-src
         - ipa-tempest-uefi-redfish-vmedia-src