all: cleanup unused code, part 2 (#10670)

And enable U1000 check in staticcheck.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

control/controlbase/conn_test.go

@@ -7,7 +7,6 @@ import (
 	"bufio"
 	"bytes"
 	"context"
-	"crypto/rand"
 	"encoding/binary"
 	"fmt"
 	"io"
@@ -302,32 +301,6 @@ func TestConnMemoryOverhead(t *testing.T) {
 	}
 }
 
-// mkConns creates synthetic Noise Conns wrapping the given net.Conns.
-// This function is for testing just the Conn transport logic without
-// having to muck about with Noise handshakes.
-func mkConns(s1, s2 net.Conn) (*Conn, *Conn) {
-	var k1, k2 [chp.KeySize]byte
-	if _, err := rand.Read(k1[:]); err != nil {
-		panic(err)
-	}
-	if _, err := rand.Read(k2[:]); err != nil {
-		panic(err)
-	}
-
-	ret1 := &Conn{
-		conn: s1,
-		tx:   txState{cipher: newCHP(k1)},
-		rx:   rxState{cipher: newCHP(k2)},
-	}
-	ret2 := &Conn{
-		conn: s2,
-		tx:   txState{cipher: newCHP(k2)},
-		rx:   rxState{cipher: newCHP(k1)},
-	}
-
-	return ret1, ret2
-}
-
 type readSink struct {
 	r io.Reader