I noticed a double-() in the deprecated.rst rendering today. Fix that
one and two others in the Documentation/ tree.

Acked-by: "Paul E. McKenney" <paulmck@kernel.org> # For RCU
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200817233207.4083538-1-keescook@chromium.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>