Is it possible to remove the label on lightning:namespace components?

Yes you can set the variant attribute to "label-hidden", so your code should look like:

<lightning:input type="number" label="number" variant = "label-hidden" name="aNumberInputField"/>

If you still want to use the lightning base components without the labels you can put the display to none and the visibility to hidden like this

.THIS .slds-form-element__label {
      display : none;
      visibility : hidden;
}

The label property, for now, is mandatory on that control. It may not be a perfect fit, but the set of <ui:inputXXX> controls provide very similar functionality without the requirement for a label. You may find that you have to recreate some functionality (depending on your needs), but you'll be very nearly there from the get go.