*: Use http.Request.WithContext instead of Cancel

pkg/httputil/httputil.go

@@ -13,15 +13,6 @@ import (
 	"net/http"
 )
 
-func RequestCanceler(req *http.Request) func() {
-	ch := make(chan struct{})
-	req.Cancel = ch
-
-	return func() {
-		close(ch)
-	}
-}
-
 // GracefulClose drains http.Response.Body until it hits EOF
 // and closes it. This prevents TCP/TLS connections from closing,
 // therefore available for reuse.