[BUGFIX] FlashMessageContainer uses static flashMessageQueue

Change-Id: I1a2078d71f21a812261ee1e3a6db8f1e7e90cafb
Resolves: #46774
Related: #44593
Releases: 6.1
Reviewed-on: https://review.typo3.org/19434
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn