chore(swamp): remove always failing assert (celestiaorg#3463)

From `context.Context.Err() error` documentation
(https://pkg.go.dev/context#Context):

```
	// If Done is not yet closed, Err returns nil.
	// If Done is closed, Err returns a non-nil error explaining why:
	// Canceled if the context was canceled
	// or DeadlineExceeded if the context's deadline passed.
	// After Err returns a non-nil error, successive calls to Err return the same error.
	Err() error
```

In other words when we observe a cancelled context `Err` is always not
nil https://go.dev/play/p/2N6F75a70lK

Co-authored-by: rene <[email protected]>

nodebuilder/tests/swamp/swamp.go

@@ -126,7 +126,6 @@ func (s *Swamp) WaitTillHeight(ctx context.Context, height int64) libhead.Hash {
 	for {
 		select {
 		case <-ctx.Done():
-			require.NoError(s.t, ctx.Err())
 		case <-t.C:
 			latest, err := s.ClientContext.LatestHeight()
 			require.NoError(s.t, err)