Remove setup.py file to fully move to a modern build based on pyproject.toml (#1365)

Author: tleonhardt

pyproject.toml

@@ -313,4 +313,7 @@ docstring-code-format = false
 # enabled.
 docstring-code-line-length = "dynamic"
 
+[tool.setuptools]
+packages = ["cmd2"]
+
 [tool.setuptools_scm]