Autolink: Don't set the HTML title attribute on hashtag values when it's the same as the link value

[jamesmacwhite]

For accessibility reasons, setting a title value that's the same as the actual text value is redundant. This happens with autolinked hashtag values example:

https://github.com/twitter/twitter-text/blob/master/conformance/autolink.yml#L128-L131

On accessibility grounds running the autolinked output through WAVE flags as a "Redundant title text" warning.

Describe the solution you'd like

A title value shouldn't be set if it doesn't convey any additional advisory information about the link itself. It is better off being removed entirely, given the values are the same. Alternatively a more descriptive title value could be used, but using the title attribute is generally advised against these days for most cases due to it's different interpretation in some web browsers.