remove incorrect reference to redirect_uri

`redirect_uri` is **not** a parameter to the call that exchanges the OAuth2 code for the token. It's a parameter to an earlier call: the one that redirects the user back to the app.

data/reusables/apps/web-app-flow-exchange-code.md

@@ -5,5 +5,4 @@
    `client_id` | `string` | **Required.** The client ID for your {% data variables.product.prodname_github_app %}. The client ID is different from the app ID. You can find the client ID on the settings page for your app. For more information about navigating to the settings page for your {% data variables.product.prodname_github_app %}, see "[AUTOTITLE](/apps/maintaining-github-apps/modifying-a-github-app-registration#navigating-to-your-github-app-settings)."
    `client_secret` | `string` | **Required.** The client secret for your {% data variables.product.prodname_github_app %}. You can generate a client secret on the settings page for your app.
    `code` | `string` | **Required.** The code you received in the previous step.
-   `redirect_uri` | `string` | The URL in your application where users will be sent after authorization. This must be an exact match to one of the URLs you provided as a "Callback URL" when setting up your {% data variables.product.prodname_github_app %} and can't contain any additional parameters.
    `repository_id` | `string` | The ID of a single repository that the user access token can access. If the {% data variables.product.prodname_github_app %} or user cannot access the repository, this will be ignored. Use this parameter to restrict the access of the user access token further.