chore: gitignore the API reference (#950)

## Description

The generated API reference under docs/docs/06-api-reference/ is
regenerated at build time by docusaurus-plugin-typedoc (runs as part of
yarn build), so there's no reason to track it in git. This removes the
files, gitignores the directory, and deletes the now-redundant
api-reference-up-to-date-check CI workflow.

### Introduces a breaking change?

- [ ] Yes
- [ ] No

### Type of change

- [ ] Bug fix (change which fixes an issue)
- [ ] New feature (change which adds functionality)
- [ ] Documentation update (improves or adds clarity to existing
documentation)
- [ ] Other (chores, tests, code style improvements etc.)

### Tested on

- [ ] iOS
- [ ] Android

### Testing instructions

<!-- Provide step-by-step instructions on how to test your changes.
Include setup details if necessary. -->

### Screenshots

<!-- Add screenshots here, if applicable -->

### Related issues

<!-- Link related issues here using #issue-number -->

### Checklist

- [ ] I have performed a self-review of my code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have updated the documentation accordingly
- [ ] My changes generate no new warnings

### Additional notes

<!-- Include any additional information, assumptions, or context that
reviewers might need to understand this PR. -->

Author: chmjkb

.github/workflows/api-reference-up-to-date-check.yml

@@ -90,6 +90,12 @@ android/generated
 apps/*/ios/
 apps/*/android/
 
+# generated TypeDoc API reference (regenerated at build time)
+docs/docs/06-api-reference/
+
+# integration test model assets
+packages/react-native-executorch/common/rnexecutorch/tests/integration/assets/models/
+
 # custom
 *.tgz
 Makefile