[Bug]: `@babel/register` has incorrect `sourceMaps` default settings

### 💻

- [ ] Would you like to work on a fix?

### How are you using Babel?

@babel/register or @babel/node

### Input code

Any code.

### Configuration file name

babel.config.js

### Configuration

```js
module.exports = {
sourceMaps: undefined
};
```

### Current and expected behavior

**Current Behavior**

`@babel/register` in [this line](https://github.com/babel/babel/blob/master/packages/babel-register/src/node.js#L64) sets the default to `"both"`:

`sourceMaps: opts.sourceMaps === undefined ? "both" : opts.sourceMaps`

**Expected Behavior**

[According to the documentation](https://babeljs.io/docs/en/options#sourcemaps), the default should be `false`.

### Environment

@babel/register: 7.10.1

### Possible solution

Change code to:

```
sourceMaps: opts.sourceMaps === undefined ? false : opts.sourceMaps
```

### Additional context

_No response_

Start at packages/babel-register/src/node.js, specifically the sourceMaps default around line 64, and compare it with the documented default in the Babel options documentation. Done means @babel/register uses false when sourceMaps is undefined while preserving an explicitly supplied value.

Written by the indexing model from the issue text.