Enable back setuptools automatic discovery

This reverts commit 8a5fa22, which was
introduced as a workaround for an issue RPM build system
(rpm-software-management/rpm#2532) but now
poses problems with recent setuptools versions that warn about missing
packages: #411

Now that the RPM issue got resolved, it seems safe to get back to
automatic discovery as this resolves the later issue in a more
future-proof way than explicitly listing packages.

pyproject.toml

@@ -84,8 +84,8 @@ Homepage = "https://github.com/dalibo/pg_activity"
 [tool.setuptools.dynamic]
 version = { attr = "pgactivity.__version__" }
 
-[tool.setuptools]
-packages = ["pgactivity"]
+[tool.setuptools.packages.find]
+where = ["."]
 
 [tool.black]
 line-length = 88