Add deregister ability to completions and contexts (#364)

* feat: add deregister methods to completions and dependencies

* fix: change unregister to deregister

* feat: add javadocs to deregisterCompleition

* fix: add throws to javadocs for dependency methods

* fix: missing negation thanks @JOO200

* fix: change deregister -> unregister

* Fix missed rename of deregister to unregister

---------

Co-authored-by: chickeneer <emcchickeneer@gmail.com>

core/src/main/java/co/aikar/commands/CommandCompletions.java

@@ -82,6 +82,20 @@ public class CommandCompletions<C extends CommandCompletionContext> {
         return this.completionMap.put(prepareCompletionId(id), handler);
     }
 
+    /**
+     * Unregister a completion handler.
+     * @param id
+     * @return
+     * @throws IllegalStateException If the completion couldn't be found
+     */
+    public CommandCompletionHandler unregisterCompletion(String id) {
+        if (!this.completionMap.containsKey(id)) {
+            throw new IllegalStateException("The supplied key " + id + " does not exist in any completions");
+        }
+
+        return this.completionMap.remove(id);
+    }
+
     /**
      * Registr a completion handler to provide command completions based on the user input.
      * This handler is declared to be safe to be executed asynchronously.

core/src/main/java/co/aikar/commands/CommandManager.java

@@ -532,6 +532,31 @@ public abstract class CommandManager<
 
         dependencies.put(clazz, key, instance);
     }
+    
+    /**
+     * Unregisters an instance of the class, it will no longer be able to be injected
+     * 
+     * @param clazz the class the injector should look for to remove
+     * @throws IllegalStateException If the dependency was not found.
+     */
+    public <T> void unregisterDependency(Class<? extends T> clazz) {
+        unregisterDependency(clazz, clazz.getName());
+    }
+
+    /**
+     * Unregisters an instance of the class, it will no longer be able to be injected
+     * 
+     * @param clazz the class the injector should look for to remove
+     * @param key   the key which needs to be present if that
+     * @throws IllegalStateException If the dependency was not found.
+     */
+    public <T> void unregisterDependency(Class<? extends T> clazz, String key) {
+        if (!dependencies.containsKey(clazz, key)) {
+            throw new IllegalStateException("Unable to unregister a dependency of " + clazz.getName() + " with the key " + key + " because it wasn't registered");
+        }
+
+        dependencies.remove(clazz, key);
+    }
 
     /**
      * Attempts to inject instances of classes registered with {@link CommandManager#registerDependency(Class, Object)}