lib: Remove osutil.Remove & osutil.RemoveAll (fixes #3513)

These are no longer required with Go 1.7. Change made by removing the
functions, doing a global s/osutil.Remove/os.Remove/.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3514

lib/versioner/staggered.go

@@ -165,7 +165,7 @@ func (v Staggered) expire(versions []string) {
 			continue
 		}
 
-		if err := osutil.Remove(file); err != nil {
+		if err := os.Remove(file); err != nil {
 			l.Warnf("Versioner: can't remove %q: %v", file, err)
 		}
 	}

lib/versioner/trashcan.go

@@ -144,7 +144,7 @@ func (t *Trashcan) cleanoutArchive() error {
 			// directory was empty and try to remove it. We ignore failure for
 			// the time being.
 			if currentDir != "" && filesInDir == 0 {
-				osutil.Remove(currentDir)
+				os.Remove(currentDir)
 			}
 			currentDir = path
 			filesInDir = 0
@@ -153,7 +153,7 @@ func (t *Trashcan) cleanoutArchive() error {
 
 		if info.ModTime().Before(cutoff) {
 			// The file is too old; remove it.
-			osutil.Remove(path)
+			os.Remove(path)
 		} else {
 			// Keep this file, and remember it so we don't unnecessarily try
 			// to remove this directory.
@@ -169,7 +169,7 @@ func (t *Trashcan) cleanoutArchive() error {
 	// The last directory seen by the walkFn may not have been removed as it
 	// should be.
 	if currentDir != "" && filesInDir == 0 {
-		osutil.Remove(currentDir)
+		os.Remove(currentDir)
 	}
 	return nil
 }