Remove all utf-8 deprecated warning.

Script used for that made by @simonsapin.
here:
https://www.reddit.com/r/rust/comments/2p3b3s/convert_to_uabcd12_style_unicode_escapes/

Copy of the script here

```bash
git grep -l '\\u' | xargs sed -i \
    -e 's/\\u000\([0-9a-fA-F]\)/\\u{\1}/g' \
    -e 's/\\u00\([0-9a-fA-F]\{2\}\)/\\u{\1}/g' \
    -e 's/\\u0\([0-9a-fA-F]\{3\}\)/\\u{\1}/g' \
    -e 's/\\u\([0-9a-fA-F]\{4\}\)/\\u{\1}/g' \
    -e 's/\\U0000000\([0-9a-fA-F]\)/\\u{\1}/g' \
    -e 's/\\U000000\([0-9a-fA-F]\{2\}\)/\\u{\1}/g' \
    -e 's/\\U00000\([0-9a-fA-F]\{3\}\)/\\u{\1}/g' \
    -e 's/\\U0000\([0-9a-fA-F]\{4\}\)/\\u{\1}/g' \
    -e 's/\\U000\([0-9a-fA-F]\{5\}\)/\\u{\1}/g' \
    -e 's/\\U00\([0-9a-fA-F]\{6\}\)/\\u{\1}/g' \
    -e 's/\\U0\([0-9a-fA-F]\{7\}\)/\\u{\1}/g' \
    -e 's/\\U\([0-9a-fA-F]\{8\}\)/\\u{\1}/g'
```
auto merge of #19988 : darnuria/rust/fix-unicode-deprecated, r=alexcrichton

Script used for that made by @simonsapin.
here:
https://www.reddit.com/r/rust/comments/2p3b3s/convert_to_uabcd12_style_unicode_escapes/

Copy here

```bash
git grep -l '\\u' | xargs sed -i \
    -e 's/\\u000\([0-9a-fA-F]\)/\\u{\1}/g' \
    -e 's/\\u00\([0-9a-fA-F]\{2\}\)/\\u{\1}/g' \
    -e 's/\\u0\([0-9a-fA-F]\{3\}\)/\\u{\1}/g' \
    -e 's/\\u\([0-9a-fA-F]\{4\}\)/\\u{\1}/g' \
    -e 's/\\U0000000\([0-9a-fA-F]\)/\\u{\1}/g' \
    -e 's/\\U000000\([0-9a-fA-F]\{2\}\)/\\u{\1}/g' \
    -e 's/\\U00000\([0-9a-fA-F]\{3\}\)/\\u{\1}/g' \
    -e 's/\\U0000\([0-9a-fA-F]\{4\}\)/\\u{\1}/g' \
    -e 's/\\U000\([0-9a-fA-F]\{5\}\)/\\u{\1}/g' \
    -e 's/\\U00\([0-9a-fA-F]\{6\}\)/\\u{\1}/g' \
    -e 's/\\U0\([0-9a-fA-F]\{7\}\)/\\u{\1}/g' \
    -e 's/\\U\([0-9a-fA-F]\{8\}\)/\\u{\1}/g'
```