Otherwise all the clients only using control/controlhttp for the
ts2021 HTTP client were also pulling in WebSocket libraries, as the
server side always needs to speak websockets, but only GOOS=js clients
speak it.
This doesn't yet totally remove the websocket dependency on Linux because
Linux has a envknob opt-in to act like GOOS=js for manual testing and force
the use of WebSockets for DERP only (not control). We can put that behind
a build tag in a future change to eliminate the dep on all GOOSes.
Updates #1278
Change-Id: I4f60508f4cad52bf8c8943c8851ecee506b7ebc9
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
