Remove FileMode.getMode()

The octal value associated to `FileMode` is not very useful to users, since it is only used internally, when generating the tree id. Therefore we can probably remove the getter for now.

src/main/java/org/apache/commons/codec/digest/GitIdentifiers.java

@@ -180,29 +180,14 @@ private static FileMode get(final Path path) {
             return REGULAR;
         }
 
-        /**
-         * The octal mode as used by Git.
-         */
-        private final String mode;
-
         /**
          * Serialized {@code mode}: since this is mutable, it must remain private.
          */
         private final byte[] modeBytes;
 
         FileMode(final String mode) {
-            this.mode = mode;
             this.modeBytes = mode.getBytes(StandardCharsets.US_ASCII);
         }
-
-        /**
-         * Gets the octal mode as used by Git.
-         *
-         * @return The octal mode.
-         */
-        public String getMode() {
-            return mode;
-        }
     }
 
     /**