Revert "Test suite: mark "Scenario: Tails shuts down on USB boot medium removal" as fragile."

This reverts commit 718d76f9.

refs: #10720

features/checks.feature

@@ -90,8 +90,6 @@ Feature: Various checks
     When I eject the boot medium
     Then Tails eventually shuts down
 
-  #10720
-  @fragile
   Scenario: Tails shuts down on USB boot medium removal
     Given I have started Tails without network from a USB drive without a persistent partition and logged in
     When I eject the boot medium