Remove unnecessary SanitizeHTML from code (#29575)

* "mail/issue/default.tmpl": the body is rendered by backend
`markdown.RenderString() HTML`, it has been already sanitized
* "repo/settings/webhook/base_list.tmpl": "Description" is prepared by
backend `ctx.Tr`, it doesn't need to be sanitized

templates/repo/settings/webhook/base_list.tmpl

@@ -10,7 +10,7 @@
 <div class="ui attached segment">
 	<div class="ui list">
 		<div class="item">
-			{{.Description | SanitizeHTML}}
+			{{.Description}}
 		</div>
 		{{range .Webhooks}}
 			<div class="item truncated-item-container">