Remove Rust hydration

[gadomski]

I moved the Rust+Python stuff to a micro-repo: https://github.com/gadomski/hydraters. That lets us remove all the maturin and other Rust build-y stuff from this repo.

For CI, we'll need to:

• Set up trusted publishing in PyPI. You could make me a maintainer in pypi and I'd be happy to take care of it (https://pypi.org/project/pypgstac/)
• Create a pypi environment (e.g. https://github.com/stac-utils/stac-asset/deployments/PyPI)

[gadomski]

I verified that hatchling grabs the sql files:

$ python -m build src/pypgstac
$ tar tvf src/pypgstac/dist/pypgstac-0.9.1.dev0.tar.gz | grep sql -m 5 
-rw-r--r--  0 0      0          86 Feb  1  2020 pypgstac-0.9.1.dev0/src/pypgstac/migrations/pgstac.0.1.9-0.2.3.sql
-rw-r--r--  0 0      0       35445 Feb  1  2020 pypgstac-0.9.1.dev0/src/pypgstac/migrations/pgstac.0.1.9.sql
-rw-r--r--  0 0      0          86 Feb  1  2020 pypgstac-0.9.1.dev0/src/pypgstac/migrations/pgstac.0.2.3-0.2.4.sql
-rw-r--r--  0 0      0       35445 Feb  1  2020 pypgstac-0.9.1.dev0/src/pypgstac/migrations/pgstac.0.2.3.sql
-rw-r--r--  0 0      0        7132 Feb  1  2020 pypgstac-0.9.1.dev0/src/pypgstac/migrations/pgstac.0.2.4-0.2.5.sql