Make SVG size argument optional (#12814)

Now defaults to 16 on both frontend and backend.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/repo/empty.tmpl

@@ -35,7 +35,7 @@
 								{{end}}
 								{{if not (and $.DisableHTTP $.DisableSSH)}}
 									<button class="ui basic button poping up clipboard" id="clipboard-btn" data-original="{{.i18n.Tr "repo.copy_link"}}" data-success="{{.i18n.Tr "repo.copy_link_success"}}" data-error="{{.i18n.Tr "repo.copy_link_error"}}" data-content="{{.i18n.Tr "repo.copy_link"}}" data-variation="inverted tiny" data-clipboard-target="#repo-clone-url">
-										{{svg "octicon-clippy" 16}}
+										{{svg "octicon-clippy"}}
 									</button>
 								{{end}}
 							</div>