dev-contributing.txt: Fix formatting of list in "Deprecated Features" section
dev-contributing.txt: Fix formatting of list in "Deprecated Features" section

Change-Id: Ie279a7df0bae197d806202ffd5787bf4523317a7
Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>

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