Fix doc link (again)

Fix doc link (again)

Similar to #52404. The link for comparison:

-   https://doc.rust-lang.org/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-sized (broken)

-   https://doc.rust-lang.org/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait (correct, stable 2nd ed)

-   https://doc.rust-lang.org/nightly/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait (correct, nightly 2nd ed)

-   https://doc.rust-lang.org/nightly/book/2018-edition/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait (correct, nightly 2018 ed)

This commit is the result of (first) searching via ripgrep (0.8.1 -SIMD -AVX):

    rg -l dynamically-sized-types-and-sized

and then replacing all relevant occurrences via:

    find src/{libcore,test/ui} -type f -print0 | xargs -0 sed -i.bak \
      s/dynamically-sized-types-and-sized/dynamically-sized-types-and-the-sized-trait/g
    find src/{libcore,test/ui} -type f -name '*.bak' -print0 | xargs -0 rm

(Note: Tested on on macOS 10.13 (BSD). `sed -i.bak` should work on Linux
(GNU sed) as well, but not tested.)