Remove unused *tag methods from AddressBook

Remove unused addTag() removeTag() and containsTag()
from AddressBook class

src/seedu/addressbook/data/AddressBook.java

@@ -82,29 +82,13 @@ public void addPerson(Person toAdd) throws DuplicatePersonException {
         allPersons.add(toAdd);
     }
 
-    /**
-     * Adds a tag to the list of tags present in the address book.
-     *
-     * @throws DuplicateTagException if an equivalent tag already exists.
-     */
-    public void addTag(Tag toAdd) throws DuplicateTagException {
-        allTags.add(toAdd);
-    }
-
     /**
      * Checks if an equivalent person exists in the address book.
      */
     public boolean containsPerson(ReadOnlyPerson key) {
         return allPersons.contains(key);
     }
 
-    /**
-     * Checks if an equivalent person exists in the address book.
-     */
-    public boolean containsTag(Tag key) {
-        return allTags.contains(key);
-    }
-
     /**
      * Removes the equivalent person from the address book.
      *
@@ -114,15 +98,6 @@ public void removePerson(ReadOnlyPerson toRemove) throws PersonNotFoundException
         allPersons.remove(toRemove);
     }
 
-    /**
-     * Removes the equivalent Tag from the address book.
-     *
-     * @throws TagNotFoundException if no such Tag could be found.
-     */
-    public void removeTag(Tag toRemove) throws TagNotFoundException {
-        allTags.remove(toRemove);
-    }
-
     /**
      * Clears all persons and tags from the address book.
      */