Move internal modules to “internal” folder.

.internal/baseUnset.js

@@ -0,0 +1,20 @@
+import castPath from './.internal/castPath.js';
+import last from './last.js';
+import parent from './.internal/parent.js';
+import toKey from './.internal/toKey.js';
+
+/**
+ * The base implementation of `unset`.
+ *
+ * @private
+ * @param {Object} object The object to modify.
+ * @param {Array|string} path The property path to unset.
+ * @returns {boolean} Returns `true` if the property is deleted, else `false`.
+ */
+function baseUnset(object, path) {
+  path = castPath(path, object);
+  object = parent(object, path);
+  return object == null || delete object[toKey(last(path))];
+}
+
+export default baseUnset;