fix(amazonq): remove Welcome Walkthrough Security Scan Feature (#8246)

## Problem
In the Amazon Q Welcome Walkthrough, the "Scan your current project"
button under "Check for security vulnerabilities" feature is
non-functional and does not initiate any scanning process when clicked.

#### Steps to Reproduce

- Click the 3-dot menu (⋯) above the chat interface
- Select "Help" from the dropdown menu
- Choose "Welcome Walkthrough" option
- Navigate to "Check for security vulnerabilities" section
- Click the "Scan your current project" button

<img width="2778" height="1896" alt="image"
src="https://github.com/user-attachments/assets/3e1a271a-c617-4e51-ae11-3fa538e54c3b"
/>

## Solution

- Remove this user experience as this is a part of agentic chat
experience.
---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

---------

Co-authored-by: seshubaws <[email protected]>

Author: laileni-aws

packages/amazonq/package.json

@@ -1470,17 +1470,6 @@
                         },
                         "completionEvents": []
                     },
-                    {
-                        "id": "aws.amazonq.walkthrough.securityScan",
-                        "title": "Check for security vulnerabilities",
-                        "description": "Amazon Q scans your code to identify security vulnerabilities and suggests fixes.\n\nStart a scan from the status bar menu.\n\n[Scan your current project](command:_aws.amazonq.walkthrough.securityScanExample)\n\nIdentifies vulnerabilities in Python, Typescript, Ruby, AWS CDK, and [more](https://docs.aws.amazon.com/amazonq/latest/qdeveloper-ug/q-language-ide-support.html#security-scans-language-support)",
-                        "media": {
-                            "markdown": "./resources/walkthrough/amazonq/scans.md"
-                        },
-                        "completionEvents": [
-                            "onCommand:_aws.amazonq.walkthrough.securityScanExample"
-                        ]
-                    },
                     {
                         "id": "aws.amazonq.walkthrough.settings",
                         "title": "Access actions and options",