all: remove unused code

Removed most of the unused code found by an automated tool (the
'unused' tool from https://github.com/dominikh/go-tools).

I did not remove some unused fields in structs and unused methods
because they need more investigation (maybe they were meant to be
used or will in the future).

Change-Id: Ibe048ce22624b609a4067479766d37cceaf6243d
Reviewed-on: https://upspin-review.googlesource.com/10320
Reviewed-by: David Presotto <presotto@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/filesystem/dir.go b/filesystem/dir.go
index 5981477..d62dc16 100644
--- a/filesystem/dir.go
+++ b/filesystem/dir.go
@@ -28,8 +28,6 @@
 }
 
 func (s dirServer) Dial(cfg upspin.Config, e upspin.Endpoint) (upspin.Service, error) {
-	const op = "store/filesystem.Dial"
-
 	dialed := *s.Server
 	dialed.user = cfg
 	return dirServer{&dialed}, nil
diff --git a/filesystem/store.go b/filesystem/store.go
index a46c544..77610f2 100644
--- a/filesystem/store.go
+++ b/filesystem/store.go
@@ -23,8 +23,6 @@
 }
 
 func (s storeServer) Dial(cfg upspin.Config, e upspin.Endpoint) (upspin.Service, error) {
-	const op = "store/filesystem.Dial"
-
 	dialed := *s.Server
 	dialed.user = cfg
 	return storeServer{&dialed}, nil