Remove version checks in `brian2.__init__.py`?

[mstimberg]

When importing the brian2 package, we check a few packages for outdated versions:

brian2/brian2/__init__.py

Lines 74 to 100 in 4886c46

	# Check for outdated dependency versions
	def _check_dependency_version(name, version):
	from packaging.version import Version
	from .core.preferences import prefs
	from .utils.logger import get_logger
	import sys
	logger = get_logger(__name__)
	module = sys.modules[name]
	if not isinstance(module.__version__, str): # mocked module
	return
	if not Version(module.__version__) >= Version(version):
	message = f'{name} is outdated (got version {module.__version__}, need version {version})'
	if prefs.core.outdated_dependency_error:
	raise ImportError(message)
	else:
	logger.warn(message, 'outdated_dependency')
	def _check_dependency_versions():
	for name, version in [('numpy', '1.10'),
	('sympy', '1.2'),
	('jinja2', '2.7')]:
	_check_dependency_version(name, version)
	_check_dependency_versions()

I'm not entirely convinced anymore that this is a good idea, so maybe we should simply remove these checks. But it would be good to have a look first how/if other packages are handling this. If we keep this, we should at least make sure that the checked requirements stay in sync with the actual requirements, by reading them in from some canonical source (requirements.txt, pyproject.toml, ...).

[bdevans]

Yes, I agree that this needs to be read in from another source if you want to keep it but provided the installed packages meet the minimum requirements to install & run Brian, maybe this should just be left to pip or conda to nag users to upgrade? The main reason I can imagine for this scenario (recommending but not requiring an upgrade) would be for better performance, however if it makes that much of a difference, maybe we should just bump the minimum requirements?