wiki: reuse selectable style for wiki (#35990)

This patch amends #27507.

Since #35072, `selectable` css
class can be used for providing hover effect for tables. This patch let
the wiki page be able to make use of that css class, and we can safely
remove the custom css for this purpose.

Behavior is not changed.

----

Side note: I made this patch locally months ago but completely forget to
submit it as a PR 😂

Author: BLumia

templates/repo/wiki/pages.tmpl

@@ -11,7 +11,7 @@
 			</span>
 		</h2>
 		{{if $.Permission.IsAdmin}}<div>{{ctx.Locale.Tr "repo.default_branch"}}: {{.Repository.DefaultWikiBranch}}</div>{{end}}
-		<table class="ui table wiki-pages-list">
+		<table class="ui table selectable wiki-pages-list">
 			<tbody>
 				{{range .Pages}}
 					<tr>

web_src/css/repo/wiki.css

@@ -1,7 +1,3 @@
-.repository.wiki .wiki-pages-list tr:hover {
-  background-color: var(--color-hover);
-}
-
 .repository.wiki .wiki-pages-list .wiki-git-entry {
   margin-left: 10px;
   display: none;