simplify exposed APi

src/utils/StructStore.js

@@ -263,16 +263,6 @@ export const replaceStruct = (store, struct, newStruct) => {
   structs[findIndexSS(structs, struct.id.clock)] = newStruct
 }
 
-/**
- * @param {StructStore} store
- * @param {ID} id
- * @return {boolean}
- *
- * @private
- * @function
- */
-export const exists = (store, id) => id.clock < getState(store, id.client)
-
 /**
  * Read StateMap from Decoder and return as Map
  *