Drop s390x builds

[mallardduck]

Because k8s removed builds for s390x we will too

[mallardduck]

/backport NONE release/v2.0

[mallardduck]

/backport NONE release/v2.0

[github-actions]

Not creating port PR, there was an error running git am -3:

Applying: Because k8s removed builds for s390x we will too
Using index info to reconstruct a base tree...
M	hack/make/deps.mk
Falling back to patching base and 3-way merge...
Auto-merging hack/make/deps.mk
CONFLICT (content): Merge conflict in hack/make/deps.mk
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"
Patch failed at 0001 Because k8s removed builds for s390x we will too