Remove services deleted from core

See https://github.com/laravel/framework/pull/28441 and https://github.com/laravel/framework/pull/28442

config/filesystems.php

@@ -37,7 +37,7 @@ return [
     | may even configure multiple disks of the same driver. Defaults have
     | been setup for each driver as an example of the required options.
     |
-    | Supported Drivers: "local", "ftp", "sftp", "s3", "rackspace"
+    | Supported Drivers: "local", "ftp", "sftp", "s3"
     |
     */
 

config/mail.php

@@ -11,8 +11,8 @@ return [
     | sending of e-mail. You may specify which one you're using throughout
     | your application here. By default, Laravel is setup for SMTP mail.
     |
-    | Supported: "smtp", "sendmail", "mailgun", "mandrill", "ses",
-    |            "sparkpost", "postmark", "log", "array"
+    | Supported: "smtp", "sendmail", "mailgun", "ses",
+    |            "postmark", "log", "array"
     |
     */
 

config/services.php

@@ -8,7 +8,7 @@ return [
     |--------------------------------------------------------------------------
     |
     | This file is for storing the credentials for third party services such
-    | as Stripe, Mailgun, SparkPost and others. This file provides a sane
+    | as Stripe, Mailgun, Postmark and others. This file provides a sane
     | default location for this type of information, allowing packages
     | to have a conventional place to find your various credentials.
     |
@@ -30,10 +30,6 @@ return [
         'region' => env('AWS_DEFAULT_REGION', 'us-east-1'),
     ],
 
-    'sparkpost' => [
-        'secret' => env('SPARKPOST_SECRET'),
-    ],
-
     'stripe' => [
         'model' => App\User::class,
         'key' => env('STRIPE_KEY'),