Remove checkbuild job

This is now unused, remove it.

Depends-On: https://review.opendev.org/676957
Change-Id: Ic9c2979d8b3a356c2c8d8820f1947f7dd33baeeb

.zuul.yaml

@@ -29,17 +29,6 @@
         ZUUL_UUID: '{{ zuul.build }}'
         ZUUL_NEWREF: '{{ zuul.ref }}'
 
-- job:
-    # TODO(AJaeger): Rename to publishdocs
-    name: build-tox-manuals-checkbuild
-    parent: build-tox-manuals-base
-    description: |
-      Build manuals using "publishdocs" tox environment.
-
-      This will be removed now after all users are updated.
-    vars:
-      tox_envlist: publishdocs
-
 - job:
     name: build-tox-manuals-publishdocs
     parent: build-tox-manuals-base