rustdoc: remove unneeded CSS .content table td:first-child > a

This rule was added in c1c6175 to benefit
the module items table. However, the module items table stopped using table
tags when 6020c79 switched us over to grid
layout.

Author: notriddle

src/librustdoc/html/static/css/rustdoc.css

@@ -207,7 +207,6 @@ h1, h2, h3, h4, h5, h6,
 a.source,
 .search-input,
 .search-results .result-name,
-.content table td:first-child > a,
 .item-left > a,
 .out-of-band,
 span.since,