DefaultSettings: Remove "~~~~" from comment to fix Doxygen parse error

DefaultSettings: Remove "~~~~" from comment to fix Doxygen parse error

> /includes/DefaultSettings.php:7478:
>  warning: reached end of file while inside a ~~~ block!
>  The command that should end the block seems to be missing!

Three or more tildes in plain text results in the beginning of
a fenced code block.
http://doxygen.org/manual/markdown.html
https://michelf.ca/projects/php-markdown/extra/#fenced-code-blocks

It stopped parsing after $wgUrlProtocols and ignored the rest.
I tried to escape it in different ways but couldn't find any method
that keeps the string readable and inline. If it's important we can
put it back in an indented code block.

Change-Id: If350a917c6afaebcd45f246404b6b6195453e51e