[pub/sub] remove `deadLetterTopic` for 1.8 declarative subscriptions #7409

	name: validate-links

	on:
	push:
	branches:
	- v*
	tags:
	- v*
	pull_request:
	branches:
	- v*
	jobs:
	validate:
	runs-on: ubuntu-latest
	env:
	PYTHON_VER: 3.7
	steps:
	- uses: actions/checkout@v2
	- name: Check Microsoft URLs do not pin localized versions
	run: \|
	localized=$(find . -name '*.md' \| xargs grep -ol "\.microsoft\.com/[[:alpha:]]\{2\}-[[:alpha:]]\{2\}/") \|\| true
	if [ -z "$localized" ]; then
	echo "All Microsoft Docs links ok."
	else
	echo "The following files contain links to Microsoft Docs that pin a localized version:"
	echo $localized
	exit 1
	fi
	- name: Set up Python ${{ env.PYTHON_VER }}
	uses: actions/setup-python@v2
	with:
	python-version: ${{ env.PYTHON_VER }}
	- name: Install dependencies
	run: \|
	python3 -m pip install --upgrade pip
	pip3 install setuptools wheel twine tox mechanical-markdown
	- name: Check Markdown Files
	run: \|
	for name in `find . -name "*.md"`; do echo -e "------\n$name" ; mm.py -l $name \|\| exit 1 ;done

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