Delete unused classes

src/main/java/com/github/steveice10/mc/protocol/data/UnmappedKeyException.java

@@ -0,0 +1,13 @@
+package com.github.steveice10.mc.protocol.data;
+
+import lombok.Getter;
+
+@Getter
+public class UnmappedKeyException extends IllegalArgumentException {
+    private Enum<?> key;
+    private Class<?> valueType;
+
+    public UnmappedKeyException(Object key, Class<?> valueType) {
+        super("Key " + key + " has no mapping for value class " + valueType.getName() + ".");
+    }
+}

src/main/java/com/github/steveice10/mc/protocol/data/UnmappedValueException.java

@@ -0,0 +1,13 @@
+package com.github.steveice10.mc.protocol.data;
+
+import lombok.Getter;
+
+@Getter
+public class UnmappedValueException extends IllegalArgumentException {
+    private Object value;
+    private Class<?> keyType;
+
+    public UnmappedValueException(Object value, Class<?> keyType) {
+        super("Value " + value + " has no mapping for key class " + keyType.getName() + ".");
+    }
+}