FieldArray change triggers validation twice

## 🐛 Bug report

### Current Behavior

When Field in FieldArray changed, the validate of Field was triggered twice.
Take a look into example in code sandbox.

### Expected behavior

Validation happens only once.

### Reproducible example

https://codesandbox.io/s/formik-fieldarray-change-validation-bug-8m6l4

### Suggested solution(s)

### Additional context

### Your environment

| Software | Version(s) |
| ---------------- | ---------- |
| Formik | 2.1.1
| React | 16.12.0
| TypeScript |
| Browser |
| npm/Yarn |
| Operating System |

Start with the linked CodeSandbox reproduction using Formik 2.1.1 and React 16.12.0, then trace the FieldArray change and validation flow. Confirm where the field validation is triggered twice; done means the same change causes validation only once.

Written by the indexing model from the issue text.