chore(swamp): remove always failing assert

[cristaloleg]

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

[Wondertan]

Wow