[Feature] Remove empty onChangeConfiguration listener

[ConnorQi01]

Summary

rn-extension.ts registers a vscode.workspace.onDidChangeConfiguration listener
that calls onChangeConfiguration(), a function that has been empty since 2017
(PR #573 removed its only content but left the skeleton behind).

This dead code adds noise and registers an unnecessary event listener on every
extension activation.

Proposed change

Remove the onDidChangeConfiguration subscription and the empty onChangeConfiguration
function entirely.