Replace Boston dataset from examples and tests.

[desilinguist]

This PR closes #700.

Replace boston dataset with california dataset everywhere.

• Remove boston example and replace with new california example.
• Remove make_boston_example_data.py script and add make_california_example_data.py script instead and sub-sample the full dataset is huge.
• Remove references to boston dataset from everywhere.
• Remove boston example test data and add california example test data.
• Replace boston name in sample test data.

[codecov[bot]]

Codecov Report

Base: 96.90% // Head: 96.90% // No change to project coverage :thumbsup:

Coverage data is based on head (8f5b6f7) compared to base (c49147b). Patch coverage: 22.22% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #717 +/- ## ======================================= Coverage 96.90% 96.90% ======================================= Files 63 63 Lines 9271 9271 ======================================= Hits 8984 8984 Misses 287 287 ``` | [Impacted Files](https://codecov.io/gh/EducationalTestingService/skll/pull/717?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService) | Coverage Δ | | |---|---|---| | [examples/make\_california\_example\_data.py](https://codecov.io/gh/EducationalTestingService/skll/pull/717/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService#diff-ZXhhbXBsZXMvbWFrZV9jYWxpZm9ybmlhX2V4YW1wbGVfZGF0YS5weQ==) | `0.00% <0.00%> (ø)` | | | [skll/experiments/output.py](https://codecov.io/gh/EducationalTestingService/skll/pull/717/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService#diff-c2tsbC9leHBlcmltZW50cy9vdXRwdXQucHk=) | `97.38% <ø> (ø)` | | | [tests/test\_regression.py](https://codecov.io/gh/EducationalTestingService/skll/pull/717/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService#diff-dGVzdHMvdGVzdF9yZWdyZXNzaW9uLnB5) | `99.64% <ø> (ø)` | | | [tests/test\_examples.py](https://codecov.io/gh/EducationalTestingService/skll/pull/717/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService#diff-dGVzdHMvdGVzdF9leGFtcGxlcy5weQ==) | `98.36% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=EducationalTestingService)

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