daemon: Stop using loadAction() for retrieving unchanged actions

Several places in the code call ActionPool::loadAction() with an
invalid KConfigGroup argument, this skips the entire loading part
of the function and simply returns the existing action as is.

(ActionPool::init() has already instantiated, but not "loaded",
any applicable PowerDevil::Action objects.)

We can have a separate function signature for this separate task.
Not having to deal with this "variant" of the function will make it
easier to change the function signature of loadAction() in a later
port to KConfigXT.

Following this commit, the only remaining call site for loadAction()
is in PowerDevil::Core::loadProfile(), which indeed passes the
correct KConfigGroup to load from.