docs: remove unneeded empty lines

Author: kenjis

docs/quickstart.md

@@ -177,7 +177,6 @@ public array $matrix = [
 ];
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 ### Assign Permissions to a User
 
 Permissions can also be assigned directly to a user, regardless of what groups they belong to. This is done programatically on the `User` Entity.
@@ -253,8 +252,6 @@ if ($user->inGroup('admin', 'beta')) {
 }
 ```
 
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 ## Managing Users
 
 Shield uses a more complex user setup than many other systems, separating [User Identities](concepts.md#identities) from the user accounts themselves. This quick overview should help you feel more confident when working with users on a day-to-day basis.