node.remove() missing from DeclareKeyword and ExportKeyword

**Describe the bug**

Version: 17.0.1

When trying to call the remove-Method ([following the docs](https://ts-morph.com/manipulation/removing)) on DeclareKeyword- or ExportKeyword-Nodes, the script will crash. Furthermore, the type guard is not able to narrow the type.

**To Reproduce**

```ts
import { ts } from "ts-morph";
// [....]
if (node.isKind(ts.SyntaxKind.ExportKeyword)) {
node.remove();
// ^-------- node wil be of type Node, instead of ExportKeyword.
// Will also crash, as it doesn't have a remove-Method
// Exception has occurred: TypeError: node.remove is not a function
}
```
**Expected behavior**

The type guard should be able to narrow the type of the node after using isKind, and the calling of remove() should not crash.

Read CONTRIBUTING.md and the removing documentation, then reproduce the TypeScript snippet for DeclareKeyword and ExportKeyword. Trace the node and type definitions for both kinds and add coverage for the narrowed remove behavior; done means both guards narrow correctly and remove no longer throws.

Written by the indexing model from the issue text.