Drop support for `tag_svn_revision`

[jaraco]

Integrated support for svn revisions has been largely removed from setuptools, but due to the specific distribution option tag_svn_revision there still exists code in setuptools that's linked to Subversion. This code should be deprecated and removed, and the setuptools_svn project should implement tagging of revisions following the model exemplified by the setuptools_scm project.

[jaraco]

Release 23.1.0 deprecates the option.

[jaraco]

Release 33.0.0 failed to deploy, as either Travis is explicitly setting that value, or perhaps it's lingering in a setup.cfg file somewhere.

[jaraco]

Oy. That version failed to pass integration tests. Packages that already have tag_svn_revision = 0 in their setup.cfg, which is probably most of them, will fail on this latest tag. Thank you integration tests for blocking the release.