Remove instnce of 'mainstream' in figure role (#1700)

closes #1321, makes `figure` consistent with other role definitions which do not refer to user agents as 'mainstream user agents'

index.html

@@ -3464,7 +3464,7 @@ <h2>Definition of Roles</h2>
 			<div class="role-description">
 				<p>A perceivable <rref>section</rref> of content that typically contains a <a>graphical document</a>, images, code snippets, or example text. The parts of a <code>figure</code> MAY be user-navigable.</p>
 				<p>Authors SHOULD provide a reference to the <code>figure</code> from the main text, but the <code>figure</code> need not be displayed at the same location as the referencing element. Authors MAY reference text serving as a caption using <pref>aria-describedby</pref>. Authors MAY provide a label using <pref>aria-label</pref> or MAY reference text serving as a label using <pref>aria-labelledby</pref>.</p>
-				<p><a>Assistive technologies</a> SHOULD enable users to quickly navigate to figures. Mainstream <a>user agents</a> MAY enable users to quickly navigate to figures.</p>
+				<p><a>Assistive technologies</a> SHOULD enable users to quickly navigate to figures. <a>User agents</a> MAY enable users to quickly navigate to figures.</p>
 			</div>
 			<table class="role-features">
 				<caption>Characteristics:</caption>