Remove reference to fixed Chrome bug in accessibility docs (twbs#20145)

Refs https://bugs.chromium.org/p/chromium/issues/detail?id=454172#c22

[skip sauce]

docs/getting-started/accessibility.md

@@ -25,7 +25,7 @@ In addition, groups and toolbars should be given an explicit label, as most assi
 If your navigation contains many links and comes before the main content in the DOM, add a `Skip to main content` link before the navigation (for a simple explanation, see this [A11Y Project article on skip navigation links](http://a11yproject.com/posts/skip-nav-links)). Using the `.sr-only` class will visually hide the skip link, and the <code>.sr-only-focusable</code> class will ensure that the link becomes visible once focused (for sighted keyboard users).
 
 {% callout danger %}
-Due to long-standing shortcomings/bugs in Chrome (see [issue 454172 in the Chromium bug tracker](https://code.google.com/p/chromium/issues/detail?id=454172 "Chromium bug tracker - Issue 454172: Focus Link Target (sequential focus navigation starting point)")) and Internet Explorer (see this article on [in-page links and focus order](http://accessibleculture.org/articles/2010/05/in-page-links/)), you will need to make sure that the target of your skip link is at least programmatically focusable by adding `tabindex="-1"`.
+Due to long-standing shortcomings/bugs in Internet Explorer (see this article on [in-page links and focus order](http://accessibleculture.org/articles/2010/05/in-page-links/)), you will need to make sure that the target of your skip link is at least programmatically focusable by adding `tabindex="-1"`.
 
 In addition, you may want to explicitly suppress a visible focus indication on the target (particularly as Chrome currently also sets focus on elements with `tabindex="-1"` when they are clicked with the mouse) with `#content:focus { outline: none; }`.