Remove _customOmitClone module.

_customOmitClone.js

@@ -1,16 +0,0 @@
-import isPlainObject from './isPlainObject.js';
-
-/**
- * Used by `_.omit` to customize its `_.cloneDeep` use to only clone plain
- * objects.
- *
- * @private
- * @param {*} value The value to inspect.
- * @param {string} key The key of the property to inspect.
- * @returns {*} Returns the uncloned value or `undefined` to defer cloning to `_.cloneDeep`.
- */
-function customOmitClone(value, key) {
-  return (key !== undefined && isPlainObject(value)) ? undefined : value;
-}
-
-export default customOmitClone;