Update go.mod and vendor

vendor/github.com/moby/buildkit/util/cond/cond.go

@@ -1,40 +0,0 @@
-package cond
-
-import (
-	"sync"
-)
-
-// NewStatefulCond returns a stateful version of sync.Cond . This cond will
-// never block on `Wait()` if `Signal()` has been called after the `Wait()` last
-// returned. This is useful for avoiding to take a lock on `cond.Locker` for
-// signalling.
-func NewStatefulCond(l sync.Locker) *StatefulCond {
-	sc := &StatefulCond{main: l}
-	sc.c = sync.NewCond(&sc.mu)
-	return sc
-}
-
-type StatefulCond struct {
-	main      sync.Locker
-	mu        sync.Mutex
-	c         *sync.Cond
-	signalled bool
-}
-
-func (s *StatefulCond) Wait() {
-	s.main.Unlock()
-	s.mu.Lock()
-	if !s.signalled {
-		s.c.Wait()
-	}
-	s.signalled = false
-	s.mu.Unlock()
-	s.main.Lock()
-}
-
-func (s *StatefulCond) Signal() {
-	s.mu.Lock()
-	s.signalled = true
-	s.c.Signal()
-	s.mu.Unlock()
-}