cause memory leak when used in SSR

store.js
```
componentWillUnmount() {
if (this.props.id) removeNamedContext(this.props.id)
}
```
namedContext.js
```
componentWillUnmount() {
removeNamedContext(this.name)
}
```
context.js
```
const createContext = React.createContext
const providers = new Map()
const ProviderContext = createContext()

export function createNamedContext(name, initialState) {
const context = createContext(initialState)
providers.set(name, context)
return context
}

export function getNamedContext(name) {
return providers.get(name)
}

export function removeNamedContext(name) {
providers.delete(name)
}

```
componentWillUnmount will not execute on server side, which cause providers increase rapidly with request increase and cause memory leak.