Stray reference to deprecated managed pointers

I removed a mention of the now deprecated managed pointers

"0.9 also begins a final series of planned changes to how pointers
are treated in Rust, starting with the deprecation of the built-in
"managed pointer" type and its accompanying `@` sigil, and the
introduction of smart pointer types to the standard library."

https://mail.mozilla.org/pipermail/rust-dev/2014-January/007753.html

Changes to be committed:
  modified:   book/chapter-07.md
Just a small typo fix.

Changes to be committed:
  modified:   book/chapter-09.md