Use Bootstrap's default link style, which is recommended

@froboy

From Make links underlined by default #1684:

As per the change upstream in Bootstrap 5 twbs/bootstrap#30389

Removing the underline from links was in vogue for a while, but WebAIM recommends not doing that.

Browsers underline hypertext links by default. It is possible to remove the underline using Cascading Style Sheets (CSS), but this is a bad idea most of the time.
I agree with @froboy that Docsy should stick to the Bootstrap & recommended default.
This is in support of:
- Docsy/User-guide "skin" styles should be factored out and/or dropped in some cases #1655

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