If avast is running you won’t be able to remove the avast files or folders as the self-defence module will prevent this. Removing the file avastSvc.exe (the avast service) itself wouldn’t resolve the problem only disable avast.

Whilst uninstalling should resolve the avastSvc.exe (the avast service) using 30% CPU, but really it would be better to find why it is using that amount of CPU % that is the main avast scanning service/control but it doesn’t just run of its own accord, there is some other activity that avast is scanning.

What were you doing when this CPU activity was going on ?
Have (or did) you another Anti-Virus installed in this system, if so what was it and how did you get rid of it ?

Some information on your system spec would be helpful, Operating System, RAM and CPU ?