fix: replaced useless let (#31239)

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

packages/next/client/image.tsx

@@ -764,7 +764,7 @@ function cloudinaryLoader({
 }: DefaultImageLoaderProps): string {
   // Demo: https://res.cloudinary.com/demo/image/upload/w_300,c_limit,q_auto/turtles.jpg
   const params = ['f_auto', 'c_limit', 'w_' + width, 'q_' + (quality || 'auto')]
-  let paramsString = params.join(',') + '/'
+  const paramsString = params.join(',') + '/'
   return `${root}${paramsString}${normalizeSrc(src)}`
 }