pkg/filenotify/poller: fix Close()
pkg/filenotify/poller: fix Close()

The code in Close() that removes the watches was not working,
because it first sets `w.closed = true` and then calls w.close(),
which starts with
```
        if w.closed {
                return errPollerClosed
	}
```

Fix by setting w.closed only after calling w.remove() for all the
files being watched.

While at it, remove the duplicated `delete(w.watches, name)` code.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

jvanz/docker,maxamillion/docker,docker/docker,Mokolea/docker,dmcgowan/docker,flavio/docker,KarthikNayak/docker,Ramzec/docker,moul/docker,konstruktoid/docker-upstream,KarthikNayak/docker,paralin/docker,bearstech/moby,jlhawn/docker,thaJeztah/docker,AkihiroSuda/docker,nawawi/docker,jvanz/docker,konstruktoid/docker-1,Mokolea/docker,moul/docker,flavio/docker,cpuguy83/docker,nalind/docker,maxamillion/docker,jthelin/docker,trebonian/docker,unclejack/docker,nawawi/docker,jimjag/docker,konstruktoid/docker-upstream,flavio/docker,dmcgowan/docker,Ramzec/docker,maxamillion/docker,justincormack/docker,ibuildthecloud/docker,pradipd/moby,ibuildthecloud/docker,dims/docker,thaJeztah/docker,rremer/moby,jlhawn/docker,rancher/docker,yosifkit/docker,SvenDowideit/docker,laijs/docker,Mokolea/docker,yongtang/docker,tmp6154/docker,jameszhan/docker,yosifkit/docker,kojiromike/docker,SvenDowideit/docker,justincormack/docker,moby/moby,crosbymichael/docker,docker/docker,yosifkit/docker,yongtang/docker,tmp6154/docker,mikebrow/docker,jwhonce/docker,kojiromike/docker,dmcgowan/docker,nalind/docker,trebonian/docker,pradipd/moby,estesp/docker,Ramzec/docker,AkihiroSuda/docker,bearstech/moby,dims/docker,laijs/docker,jwhonce/docker,gnailuy/docker,cpuguy83/docker,jameszhan/docker,nawawi/docker,YuPengZTE/docker,bearstech/moby,laijs/moby,konstruktoid/docker-upstream,dims/docker,flavio/docker,Mokolea/docker,moby/moby,Ramzec/docker,scotttlin/docker,scotttlin/docker,ibuildthecloud/docker,mahak/docker,jameszhan/docker,kojiromike/docker,gnailuy/docker,djs55/docker,cpuguy83/docker,konstruktoid/docker-1,moul/docker,estesp/docker,ibuildthecloud/docker,moby/moby,moul/docker,paralin/docker,vdemeester/docker,SvenDowideit/docker,jimjag/docker,kolyshkin/moby,ibuildthecloud/docker,gnailuy/docker,jwhonce/docker,laijs/moby,konstruktoid/docker-upstream,trebonian/docker,rremer/moby,crosbymichael/docker,crosbymichael/docker,docker/docker,jlhawn/docker,nawawi/docker,mahak/docker,vdemeester/docker,YuPengZTE/docker,thaJeztah/docker,trebonian/docker,paralin/docker,jimjag/docker,justincormack/docker,mikebrow/docker,scotttlin/docker,thaJeztah/docker,rancher/docker,rancher/docker,kolyshkin/docker,moby/moby,rremer/moby,laijs/moby,yosifkit/docker,tmp6154/docker,kolyshkin/moby,djs55/docker,paralin/docker,nalind/docker,gnailuy/docker,mikebrow/docker,KarthikNayak/docker,jthelin/docker,jvanz/docker,pradipd/moby,kolyshkin/docker,vdemeester/docker,x1022as/docker,AkihiroSuda/docker,YuPengZTE/docker,kolyshkin/moby,mahak/docker,cpuguy83/docker,djs55/docker,jimjag/docker,konstruktoid/docker-1,x1022as/docker,yongtang/docker,mahak/docker,bearstech/moby,unclejack/docker,laijs/docker,AkihiroSuda/docker,x1022as/docker,estesp/docker,unclejack/docker,nalind/docker