chore: Cleanup non-functional code from terminal integration

Description

I was looking closer at the code and noticed that the command run timeout and stream read timeout in the Terminal Manager implementation are not working.

1. Stream read timeout - Only logs a message without actually stopping command execution
2. Command execution timeout - Created inside onDidEndTerminalShellExecution, which fires after the command has already exited, making it pointless

We should remove the timeout code entirely rather than fixing it:

• There is no reasonable generic timeout value that works for all commands
• Many commands produce no output on success (e.g., git add, git config, file operations like cp, mv, mkdir, or npm install --silent), making stream read timeouts impractical

How has this been tested?

• Run extension in development host
• Open Agentic chat - ask it to run some command
• command should be executed successfully

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes