you can for sure remove the components that are not in use anymore. The previous version of Solidcore is checked in the Previous branch, so absolutely no problem of removing it.
In the case with HIPS note that if you do so, you won't be able to use the ePO to send remove/uninstall task to the endpoints, but if you have already removed it, then you're good to proceed. Just remember to remove HIPS from both the Master Repository and from the Extensions.
Note that's always a good idea to perform full ePO backup before checking in or removing products following this article McAfee Corporate KB - kb66616
it also might be a good idea to export the policies for those products just for your peace of mind.