Improvement: Remove pubspec.lock

[freitzzz]

According to Google Dart guidelines:
> For library packages, don’t commit the pubspec.lock file. Regenerating the pubspec.lock file lets you test your package against the latest compatible versions of its dependencies.
https://dart.dev/guides/libraries/private-files#pubspeclock

In that sense, since overlay_webview is a package, pubspec.lock should be removed