Update configure-git-for-release-management.sh to use modern setup

With "modern" I mean what's used in later iteration of the setup.

Compare WordPress iOS,
https://github.com/wordpress-mobile/WordPress-iOS/blob/b4de5f928cd784cb85144ca469b27910666d8d30/.buildkite/commands/configure-git-for-release-management.sh
, with WooCommerce iOS
https://github.com/woocommerce/woocommerce-ios/blob/c2f38422ddb12b891afbab9962869affa7722af2/.buildkite/commands/configure-git-for-release-management.sh

.buildkite/commands/configure-git-for-release-management.sh

@@ -3,11 +3,6 @@
 # The Git command line client is not configured in Buildkite.
 # At the moment, steps that need Git access can configure it on deman using this script.
 # Later on, we should be able to configure it on the agent instead.
-
-curl -L https://api.github.com/meta | jq -r '.ssh_keys | .[]' | sed -e 's/^/github.com /' >> ~/.ssh/known_hosts
+add_host_to_ssh_known_hosts github.com
 git config --global user.email "[email protected]"
 git config --global user.name "Automattic Release Bot"
-
-# Buildkite is currently using the HTTPS URL to checkout.
-# We need to override it to be able to use the deploy key.
-git remote set-url origin [email protected]:Automattic/simplenote-ios.git