send_future is no longer needed

[hgzimmerman]

Description

I'm submitting a feature request
Put your description here

@jstarry and I have talked about removing the send_future function on ComponentLink. Our current consensus revolves around it being possible to implement this using the existing send_message function on that datatype to accomplish the same thing.

Yewtil, the utilities crate for Yew already has a replacement ready for its next release that does the same thing and just requires importing a trait to use a send_future method.

I suggest that we remove this feature from the main crate, and point users towards the utility crate.
Because yewtil is heavily feature-gated, users are free to pick and choose which features to enable, so there shouldn't be any unwanted overhead besides having to import that trait.