revert: revert to "feat(amazonq): add MCP server support (#7451)"

[ashishrp-aws]

Problem

MCP Servers feature is broken in alpha manifest and is causing regression to chat.

Solution

• reverting the feature flag to enable MCP

---

• 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.
• License: I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

• This pull request modifies code in src/* but no tests were added/updated.
  • Confirm whether tests should be added or ensure the PR description explains why tests are not required.