rustdoc: merge table { border-collapse } into .docblock table`

This was added in 5101078, to fix the
display of the module items and search results tables (see the discussion in
#86725).

Those aren't tables any more. The only remaining table is in docblock, which
needs this attribute to look right.

Author: notriddle

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

@@ -299,10 +299,6 @@ summary {
 
 /* Fix some style changes due to normalize.css 8 */
 
-table {
-	border-collapse: collapse;
-}
-
 button,
 input,
 optgroup,
@@ -690,6 +686,7 @@ pre, .rustdoc.source .example-wrap {
 	width: calc(100% - 2px);
 	overflow-x: auto;
 	display: block;
+	border-collapse: collapse;
 }
 
 .docblock table td {