ci: remove discontinued XATA_TOKEN usage (#41707)

## Summary
- Replace discontinued Xata database curl calls with `touch
~/knownfailures` in `build-client-server.yml` and
`build-client-server-count.yml` (matching the fix already applied to
`pr-cypress.yml` in e61375d297)
- Delete orphaned `app/client/cypress/xataadd.sh` and
`app/client/cypress/xatadel.sh` scripts that are not referenced by any
workflow

## Context
XATA Lite has been discontinued. The existing curl calls were silently
failing (stderr redirected to `/dev/null`), producing an empty
`~/knownfailures` file — identical behavior to the `touch` replacement.
This completes the partial cleanup started in pr-cypress.yml.

**After merging, the `XATA_TOKEN` GitHub secret can be safely removed
from the repository settings.**

## Test plan
- [ ] Verify `build-client-server` workflow runs successfully on a test
PR
- [ ] Verify `build-client-server-count` workflow runs successfully on a
test PR
- [ ] Confirm PR comment behavior for CI failures remains unchanged

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Streamlined CI/CD pipeline by simplifying test failure tracking and
validation processes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->


## Automation

/ok-to-test tags="@tag.Sanity"

<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/24066890157>
> Commit: 9982ddf168d0cfc5eb5032fa749c3649398498d1
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=24066890157&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Sanity`
> Spec:
> <hr>Tue, 07 Apr 2026 06:35:51 UTC
<!-- end of auto-generated comment: Cypress test results  -->

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>