libnetwork/resolvconf: removed unused GetIfChanged() and GetLastModified()

These functions were used in 63a7ccdd2372d87f56f7a86da07c72ea51332c2a, which was
part of Docker v1.5.0 and v1.6.0, but removed in Docker v1.7.0 when the network
stack was replaced with libnetwork in d18919e304c240df84502cdcc5ed655d92d12d4f.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 49de15cdcc14f752950ab7ef0f14fc08713f3521)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/resolvconf/resolvconf.go

@@ -85,12 +85,6 @@ var (
 	optionsRegexp     = regexp.MustCompile(`^\s*options\s*(([^\s]+\s*)*)$`)
 )
 
-var lastModified struct {
-	sync.Mutex
-	sha256   string
-	contents []byte
-}
-
 // File contains the resolv.conf content and its hash
 type File struct {
 	Content []byte
@@ -115,39 +109,6 @@ func GetSpecific(path string) (*File, error) {
 	return &File{Content: resolv, Hash: hash}, nil
 }
 
-// GetIfChanged retrieves the host /etc/resolv.conf file, checks against the last hash
-// and, if modified since last check, returns the bytes and new hash.
-// This feature is used by the resolv.conf updater for containers
-func GetIfChanged() (*File, error) {
-	lastModified.Lock()
-	defer lastModified.Unlock()
-
-	resolv, err := os.ReadFile(Path())
-	if err != nil {
-		return nil, err
-	}
-	newHash, err := hashData(bytes.NewReader(resolv))
-	if err != nil {
-		return nil, err
-	}
-	if lastModified.sha256 != newHash {
-		lastModified.sha256 = newHash
-		lastModified.contents = resolv
-		return &File{Content: resolv, Hash: newHash}, nil
-	}
-	// nothing changed, so return no data
-	return nil, nil
-}
-
-// GetLastModified retrieves the last used contents and hash of the host resolv.conf.
-// Used by containers updating on restart
-func GetLastModified() *File {
-	lastModified.Lock()
-	defer lastModified.Unlock()
-
-	return &File{Content: lastModified.contents, Hash: lastModified.sha256}
-}
-
 // FilterResolvDNS cleans up the config in resolvConf.  It has two main jobs:
 //  1. It looks for localhost (127.*|::1) entries in the provided
 //     resolv.conf, removing local nameserver entries, and, if the resulting