Remove timeout input events

Now that timeouts are stored in the event queue peeker, we can remove the
notion of timeout events altogether. Instead you may ask for an event with
a timeout, and get back none on timeout. This simplifies how input events
work.

src/input.cpp

@@ -462,10 +462,14 @@ class event_queue_peeker_t {
             return false;
         }
         // Grab a new event if we have exhausted what we have already peeked.
+        // Use either readch or readch_timed, per our param.
         if (idx_ == peeked_.size()) {
-            auto newevt = timed ? event_queue_.readch_timed() : event_queue_.readch();
-            if (newevt.is_timeout()) {
-                assert(timed && "Should only get timeouts from timed reads");
+            char_event_t newevt{L'\0'};
+            if (!timed) {
+                newevt = event_queue_.readch();
+            } else if (auto mevt = event_queue_.readch_timed()) {
+                newevt = mevt.acquire();
+            } else {
                 had_timeout_ = true;
                 return false;
             }