Avoid trying to load non-existent image URLs in tests

Fix 404 warnings from headless Chrome during tests caused by trying to
load non-existent image URLs in the anchoring regression tests.

src/annotator/anchoring/test/html-baselines/wikipedia-regression-testing.html

@@ -300,9 +300,9 @@ additional terms may apply.  By using this site, you agree to the <a href="//wik
 									</ul>
 										<ul id="footer-icons" class="noprint">
 											<li id="footer-copyrightico">
-							<a href="https://wikimediafoundation.org/"><img src="/static/images/wikimedia-button.png" srcset="/static/images/wikimedia-button-1.5x.png 1.5x, /static/images/wikimedia-button-2x.png 2x" width="88" height="31" alt="Wikimedia Foundation"/></a>						</li>
+							<a href="https://wikimediafoundation.org/"><img src="" srcset="" width="88" height="31" alt="Wikimedia Foundation"/></a>						</li>
 											<li id="footer-poweredbyico">
-							<a href="//www.mediawiki.org/"><img src="/static/images/poweredby_mediawiki_88x31.png" alt="Powered by MediaWiki" srcset="/static/images/poweredby_mediawiki_132x47.png 1.5x, /static/images/poweredby_mediawiki_176x62.png 2x" width="88" height="31"/></a>						</li>
+							<a href="//www.mediawiki.org/"><img src="" alt="Powered by MediaWiki" srcset="" width="88" height="31"/></a>						</li>
 									</ul>
 						<div style="clear:both"></div>
 		</div>