`Timer`: Remove `periodic()` and `timeout()`

### What's needed?

The names are just too confusing and we'll never find a name that can convey all the intricacies of timers in the async world.

I'll probably leave the docs about both methods as examples of how to use the timer to achieve different goals.

### Proposed solution

Remove `periodic()` and `timeout()` and force users to pass the missing ticks policies manually.