rustdoc: simplify .search-results-title CSS

By using `display: flex`, we still get the never-wrapping layout with
`#crate-search-div` maxing out and truncating its text. The title itself
winds up always filling its parent, but since `#crate-search` doesn't have
`flex-grow` set, it won't fill available space.

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

@@ -785,8 +785,7 @@ table,
 	margin-top: 0;
 	white-space: nowrap;
 	/* flex layout allows shrinking the <select> appropriately if it becomes too large */
-	display: inline-flex;
-	max-width: 100%;
+	display: flex;
 	/* make things look like in a line, despite the fact that we're using a layout
 	with boxes (i.e. from the flex layout) */
 	align-items: baseline;

src/test/rustdoc-gui/search-result-display.goml

@@ -22,7 +22,8 @@ size: (900, 900)
 
 // First we check the current width, height and position.
 assert-css: ("#crate-search", {"width": "223px"})
-assert-css: (".search-results-title", {"height": "44px", "width": "336px"})
+assert-css: (".search-results-title", {"height": "44px", "width": "640px"})
+assert-css: ("#search", {"width": "640px"})
 
 // Then we update the text of one of the `<option>`.
 text: (