Remove ImportError catching from `from contextlib import redirect_stdout`

[KevinHock]

Now that we're python 3+, we can remove the following:

detect-secrets-server/detect_secrets_server/adhoc/github/webhook.py

Lines 10 to 19 in cf25d3e

	except ImportError: # pragma: no cover
	import sys
	from contextlib import contextmanager
	@contextmanager
	def redirect_stdout(target):
	original = sys.stdout
	sys.stdout = target
	yield
	sys.stdout = original

(Still reusing some code from this project :D)

[P0intMaN]

Hello Developer,

I am new to open source contribution. I would like this to be my first contribution towards this repository.
I hope this issue is still open and do I have to take permission from moderators before contributing?

Thanks!