gui: Add addresses for disconnected devices (fixes #3340)

Also fixes an issue where the discovery cache call would only return the
newest cache entry for a given device instead of the merged addresses
from all cache entries (which is more useful).

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3344

lib/versioner/util.go

@@ -9,7 +9,6 @@ package versioner
 import (
 	"path/filepath"
 	"regexp"
-	"sort"
 )
 
 // Inserts ~tag just before the extension of the filename.
@@ -32,17 +31,3 @@ func filenameTag(path string) string {
 	}
 	return match[1]
 }
-
-func uniqueSortedStrings(strings []string) []string {
-	seen := make(map[string]struct{}, len(strings))
-	unique := make([]string, 0, len(strings))
-	for _, str := range strings {
-		_, ok := seen[str]
-		if !ok {
-			seen[str] = struct{}{}
-			unique = append(unique, str)
-		}
-	}
-	sort.Strings(unique)
-	return unique
-}