Migrate baseline images from DVC to Git LFS

[seisman]

Adresses: #4738

• Track pygmt/tests/baseline/*.png using Git LFS
• Remove all *.dvc files
• Remove dvc from environment.yml
• Remove .dvc/ and .dvcignore
• Update MANIFEST.in
• Update the Maintainers' Guide
• Update the Contributors' Guide
• Remove the dvc-diff.yml workflow, because GitHub can display diffs for LFS-tracked images directly in the web UI
• Remove the cache_dvc.yaml workflow, which was added as a workaround for Running "dvc pull" now requires authentication #4147
• Update the style_checks.yaml workflow
• Update the ci_tests.yaml workflow
• Update the ci_tests_dev.yaml workflow
• Update the release-baseline-image.yml workflow
• Ensure that source and binary distributions do not include the baseline images (run make package and ensure that the files have no PNG images).

[seisman]

The migration from DVC to Git LFS turned out to be much simpler than I initially expected. This PR completes the migration, with the only exception being updates to the Contributors’ Guide. I think those documentation changes will be easier to review in a separate PR.

[weiji14]

Thanks @seisman, glad to see all the gh actions workflows getting cleaned up, and less workarounds to maintain! I haven't checked through all the 200+ hashes, but trust that it is ok since CI is fine.

Just remember to delete the DAGSHUB_TOKEN from https://github.com/GenericMappingTools/pygmt/settings/secrets/actions after merging, and to update the doc/contributing.md later as mentioned.