Remove `sl` and component initialization from the `capmgr`

[gparmer]

The capability manager currently is part of the scheduling hierarchy. It exports the init interface, and all of its associated complexity. It uses sl to perform some of its initialization. There are assumptions in the crt that any capability manager is also a scheduler, and comparable assumptions in the composer.

The capmgr should be simple and avoid this complexity (that doubles the capmgr's size). With this change, the constructor/booter would boot up the execution for the capmgr and the scheduler, and the scheduler would take it from there.

Discussed with @WenyuanShao .