runtime: remove unnecessary check for negative sleepTicks duration

This is now fixed for every target in the previous commit.

Also see: https://github.com/tinygo-org/tinygo/pull/4239

src/runtime/runtime_rp2040.go

@@ -31,10 +31,6 @@ func nanosecondsToTicks(ns int64) timeUnit {
 }
 
 func sleepTicks(d timeUnit) {
-	if d <= 0 {
-		return
-	}
-
 	if hasScheduler {
 		// With scheduler, sleepTicks may return early if an interrupt or
 		// event fires - so scheduler can schedule any go routines now