AK+Kernel+LibELF: Remove the need for IteratorDecision::Continue

By constraining two implementations, the compiler will select the best
fitting one. All this will require is duplicating the implementation and
simplifying for the `void` case.

This constraining also informs both the caller and compiler by passing
the callback parameter types as part of the constraint
(e.g.: `IterationFunction<int>`).

Some `for_each` functions in LibELF only take functions which return
`void`. This is a minimal correctness check, as it removes one way for a
function to incompletely do something.

There seems to be a possible idiom where inside a lambda, a `return;` is
the same as `continue;` in a for-loop.

Kernel/PerformanceEventBuffer.cpp

@@ -230,7 +230,6 @@ void PerformanceEventBuffer::add_process(const Process& process, ProcessEventTyp
     process.for_each_thread([&](auto& thread) {
         [[maybe_unused]] auto rc = append_with_eip_and_ebp(process.pid(), thread.tid().value(),
             0, 0, PERF_EVENT_THREAD_CREATE, 0, 0, 0, nullptr);
-        return IterationDecision::Continue;
     });
 
     for (auto& region : process.space().regions()) {