Unused imports are generated when using fragment

**Describe the bug**
`tsc --noUnusedLocals` warn generated files because the files include unused imports when using fragment.

**To Reproduce**
Steps to reproduce the behavior:

- Sample repository: https://github.com/mizdra/graphql-code-generator-sample
```
$ git clone https://github.com/mizdra/graphql-code-generator-sample.git
$ cd graphql-code-generator-sample
$ yarn install
$ yarn run build:graphql
$ yarn run check:typecheck # tsc --noUnusedLocals
```

1. My GraphQL schema:

```graphql
type Query {
articles: [Article!]!
}
type Article {
id: ID!
title: String!
body: String!
}
```

2. My GraphQL operations:

```tsx
// ArticleListItem.tsx
export function ArticleListItem() { ... }
ArticleListItem.Fragment = gql`
fragment SimpleArticle on Article {
title
body
}
`
```

```tsx
// ArticleList.tsx
import { ArticleListItem } from './ArticleListItem'

const GET_ARTICLES = gql`
query GetArticles {
articles {
...SimpleArticle
}
}
${ArticleListItem.Fragment}
`
```

3. My `codegen.yml` config file:

```yml
overwrite: true
schema: schema.graphql
generates:
src/types.generated.ts:
- typescript
src/:
documents: 'src/**/*.{ts,tsx}'
preset: near-operation-file
presetConfig:
extension: .generated.tsx
baseTypesPath: types.generated.ts
plugins:
- typescript-operations
```

**Expected behavior**
Unused imports should be removed from generated files.

**Environment:**

- OS: macOS Mojave 10.14.6
- `@graphql-codegen/cli`: 1.6.1
- `@graphql-codegen/near-operation-file-preset`: 1.6.1
- `@graphql-codegen/typescript`: 1.6.1
- `@graphql-codegen/typescript-operations`: 1.6.1
- `typescript`: 3.5.3
- NodeJS: 12.4.0

**Additional context**