[BUG] Consistent styling for Sort filter

- The dropdowns that contain filters for issues and pull requests are
currently not styled with the `small` class, which causes a smaller font
size to be set. Remove it for the `Sort` filter to make it consistent
and make it _more_ readable.
- Resolves #2914

templates/projects/list.tmpl

@@ -25,7 +25,7 @@
 		{{template "shared/search/combo" dict "Value" .Keyword "Placeholder" (ctx.Locale.Tr "search.project_kind")}}
 	</form>
 	<!-- Sort -->
-	<div class="list-header-sort ui small dropdown type jump item">
+	<div class="list-header-sort ui dropdown type jump item">
 		<span class="text">
 			{{ctx.Locale.Tr "repo.issues.filter_sort"}}
 		</span>

templates/repo/issue/filter_list.tmpl

@@ -188,7 +188,7 @@
 {{end}}
 
 <!-- Sort -->
-<div class="list-header-sort ui small dropdown downward type jump item">
+<div class="list-header-sort ui dropdown downward type jump item">
 	<span class="text">
 		{{ctx.Locale.Tr "repo.issues.filter_sort"}}
 	</span>

templates/repo/issue/milestone/filter_list.tmpl

@@ -1,5 +1,5 @@
 <!-- Sort -->
-<div class="list-header-sort ui small dropdown type jump item">
+<div class="list-header-sort ui dropdown type jump item">
 	<span class="text">
 		{{ctx.Locale.Tr "repo.issues.filter_sort"}}
 	</span>