rustdoc: remove unnecessary max-width on headers

This code was added in 003b2bc to prevent
these headers from overlapping `.out-of-band` side items. That stopped
being a problem when 3f92ff3 switched
rustdoc over to using `float`, rather than `position: absolute`, to
implement this.

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

@@ -684,7 +684,6 @@ h2.location a {
 }
 
 .method > .code-header, .trait-impl > .code-header {
-	max-width: calc(100% - 41px);
 	display: block;
 }