Fix "could not find `wasm` in `http_client`" error

[wishawa]

The compilation conditions for wasm in http-client and in surf are currently different. This difference causes surf to sometimes (usually when running cargo check) try to re-export a module that doesn't exist, leading to the error "could not find wasm in http_client".

This PR changes to condition in surf to be the same as that in http-client.