Remove support for entry-points for all supported series

Actually the topic did stick with me and I just realized that I have defined my tiny customization module completely different than the typical trytond module is defined and used a pyproject.toml instead:

name = "bv-tryton-meta-botech"
version = "0.8.0"
authors = [
  { name="Johannes Bornhold", email="" },
description = "Meta package with Tryton adjustments for the use at bo-tech."
readme = ""
requires-python = ">=3.8"
classifiers = [
    "Programming Language :: Python :: 3",
    "License :: OSI Approved :: MIT License",
    "Operating System :: OS Independent",

meta_botech = "bv.tryton.meta_botech"

requires = ["hatchling"]
build-backend = ""

packages = ["src/bv"]

Have to admit that I am not too deep into the recent developments of packaging in Python, still, so far this works out just fine thanks to the entrypoint support.

@ced would you mind sharing a few hints about the complexities / issues around the entrypoint support? Just wondering if there may be other options to reduce the maintenance burden.