server: Remove deadcode. (#2699)

cmd/posix-errors.go

@@ -33,17 +33,6 @@ func isSysErrNotDir(err error) bool {
 	return false
 }
 
-// Check if the given error corresponds to EISDIR (is a directory)
-func isSysErrIsDir(err error) bool {
-	if pathErr, ok := err.(*os.PathError); ok {
-		switch pathErr.Err {
-		case syscall.EISDIR:
-			return true
-		}
-	}
-	return false
-}
-
 // Check if the given error corresponds to ENOTEMPTY for unix
 // and ERROR_DIR_NOT_EMPTY for windows (directory not empty)
 func isSysErrNotEmpty(err error) bool {