Feature: Add Trie.deleteWord and TrieNode.removeChild

[appleJax]

This PR adds the ability to delete words from the Trie data structure.

NOTE - when deleting a word:

• sets trieNode.isCompleteWord to false for the last character in the word
• deletes trieNodes in depth-first order (last character -> first character)
• does NOT delete trieNodes if they have children
• does NOT delete trieNodes if trieNode.isCompleteWord === true (this is to prevent substring words from being deleted)

Example usage:

const trie = new Trie();
trie.addWord('carpet');
trie.addWord('car');

trie.deleteWord('carpet');

trie.doesWordExist('carpet'); // returns false
trie.doesWordExist('car'); // returns true

Issue: #108
Refactored From PR: #168

[trekhleb]

@appleJax thank you for pull request!