#369 Delete Xenforo (XF) encryption algorithm

Rationale:
- Seems not to have been working since it was added to the codebase
- Seems not to correspond to the actual Xenforo password hashing (class does some sort of JSON extraction?)
- It would be easier to rewrite it from scratch if someone requests it later

src/test/java/fr/xephi/authme/security/crypts/XFTest.java

@@ -1,17 +0,0 @@
-package fr.xephi.authme.security.crypts;
-
-import org.junit.Ignore;
-import org.junit.Test;
-
-/**
- * Test for {@link XF}.
- */
-@Ignore
-// TODO #369: XF needs to generate a salt it is expecting
-public class XFTest {
-
-    @Test
-    public void shouldComputeHash() {
-        System.out.println(new XF().computeHash("Test", "name"));
-    }
-}