Fix: remove unnecessary type assertions in http-router Router.ts

Description:

While running yarn lint on the codebase, found unnecessary type assertions
in packages/http-router/src/Router.ts flagged by the
@typescript-eslint/no-unnecessary-type-assertion rule, and an unused import.

These assertions do not change the type of the expression and can be safely removed.

Steps to reproduce:

1. Clone the repository
2. Run yarn lint --filter=@rocket.chat/http-router
3. Observe warnings on Router.ts

Expected behavior:

No unnecessary type assertion warnings or unused import errors in Router.ts

Actual behavior:

• Line 310: as string assertion is unnecessary (TypeScript already infers string from the fallback)
• Line 317: as 101 | 204 | 205 | 304 is unnecessary (already narrowed by the isContentLess type guard)
• Line 325: as StatusCode is unnecessary
• Line 7: StatusCode is imported but never used after removing the assertion

Server Setup Information:

• Version of Rocket.Chat Server:
• License Type:
• Number of Users:
• Operating System:
• Deployment Method:
• Number of Running Instances:
• DB Replicaset Oplog:
• NodeJS Version:
• MongoDB Version:

Client Setup Information

• Desktop App or Browser Version:
• Operating System:

Additional context

Relevant logs:

Start by running yarn lint --filter=@rocket.chat/http-router and open packages/http-router/src/Router.ts. Inspect the assertions at lines 310, 317, and 325 and the unused StatusCode import at line 7. Done means the assertions and unused import are resolved and the filtered lint command reports no warnings or errors.