README: Make it more clear which managers are unmaintained

Author: DilumAluthge

README.md

@@ -2,13 +2,6 @@
 
 The `ClusterManagers.jl` package implements code for different job queue systems commonly used on compute clusters.
 
-> [!WARNING]
-> This package is not currently being actively maintained or tested.
->
-> We are in the process of splitting this package up into multiple smaller packages, with a separate package for each job queue systems.
->
-> We are seeking maintainers for these new packages. If you are an active user of any of the job queue systems listed below and are interested in being a maintainer, please open a GitHub issue - say that you are interested in being a maintainer, and specify which job queue system you use.
-
 ## Available job queue systems
 
 ### In this package