chore:delete unused files (#36368)

## Description
I used [knip](https://knip.dev/) to identify unused files. There will be
a few more related PRs, after that I will add CI check for this.

Fixes #35778

Related EE PR appsmithorg/appsmith-ee#5165

## Automation

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

### 🔍 Cypress test results
<!-- This is an auto-generated comment: Cypress test results  -->
> [!TIP]
> 🟢 🟢 🟢 All cypress tests have passed! 🎉 🎉 🎉
> Workflow run:
<https://github.com/appsmithorg/appsmith/actions/runs/10940962461>
> Commit: 3174957
> <a
href="https://internal.appsmith.com/app/cypress-dashboard/rundetails-65890b3c81d7400d08fa9ee5?branch=master&workflowId=10940962461&attempt=1"
target="_blank">Cypress dashboard</a>.
> Tags: `@tag.Sanity`
> Spec:
> <hr>Thu, 19 Sep 2024 12:55:41 UTC
<!-- end of auto-generated comment: Cypress test results  -->


## Communication
Should the DevRel and Marketing teams inform users about this change?
- [ ] Yes
- [x] No

app/client/knip.json

@@ -0,0 +1,14 @@
+{
+  "entry": ["src/index.tsx"],
+  "project": ["src/**/*.tsx"],
+  "ignore": [
+    "packages/**/stories/**",
+    "packages/**/chromatic/**",
+    "packages/design-system/widgets/src/testing/**",
+    "**/*.stories.tsx",
+    "packages/rts/build.js",
+    "packages/design-system/ads/src/Documentation/**",
+    "src/components/designSystems/blueprintjs/**",
+    "packages/design-system/ads/plopfile.mjs"
+  ]
+}

app/client/package.json

@@ -354,6 +354,7 @@
     "jest-environment-jsdom": "^27.4.1",
     "jest-styled-components": "^7.0.8",
     "json5": "^2.2.3",
+    "knip": "^5.30.2",
     "lint-staged": "^14.0.1",
     "msw": "^0.28.0",
     "pg": "^8.11.3",