Remove context.Context from request.Request (#2726)

* Remove context.Context from request.Request

This removes the context from request.Request and makes all the changes
in the code to make it compile again. It's all mechanical. It did
unearth some weirdness in that the context was kept in handler structs
which may cause havoc with concurrently handling of requests.

Fixes #2721

Signed-off-by: Miek Gieben <miek@miek.nl>

* Make test compile

Signed-off-by: Miek Gieben <miek@miek.nl>

request/request.go

@@ -2,7 +2,6 @@
 package request
 
 import (
-	"context"
 	"net"
 	"strings"
 
@@ -19,12 +18,9 @@ type Request struct {
 	// Optional lowercased zone of this query.
 	Zone string
 
-	Context context.Context
-
 	// Cache size after first call to Size or Do.
 	size int
 	do   *bool // nil: nothing, otherwise *do value
-	// TODO(miek): opt record itself as well?
 
 	// Caches
 	name      string // lowercase qname.