[DOC]: build.md is out of date

[harrism]

Version

23.06

On which installation method(s) does this occur?

No response

Describe the issue

cuspatial/doc/source/developer_guide/build.md is a bit out of date. It refers to nonexistent tests and the shapefile reader.

I think we can also delete the cuspatial/test_fixtures directory because it only contains shapefiles that were used by the shapefile reader test, which is now removed.

Minimum reproducible example

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Relevant log output

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Environment details

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Other/Misc.

No response