Move licenses.txt to /assets directory (#26866)

Now that we have the `/assets` directory, we can put`licenses.txt`
directly into it instead of incorrect `/js` path which was previously
only done to avoid reserving a username.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

templates/base/footer_content.tmpl

@@ -23,7 +23,7 @@
 				{{end}}
 			</div>
 		</div>
-		<a href="{{AssetUrlPrefix}}/js/licenses.txt">{{.locale.Tr "licenses"}}</a>
+		<a href="{{AssetUrlPrefix}}/licenses.txt">{{.locale.Tr "licenses"}}</a>
 		{{if .EnableSwagger}}<a href="{{AppSubUrl}}/api/swagger">API</a>{{end}}
 		{{template "custom/extra_links_footer" .}}
 	</div>