Remove the required class from optional ssh port in installation page (#5428)

the ssh port is optional during the installation process. The
translations even mention that it is optional and can be blank. Right
now it has the `required` class which creates the red `*` behind the
field caption - used for required fields.
If you leave it blank, the SSH option is disabled
(not touched by this PR)

Signed-off-by: Roman <romaaan.git@gmail.com>

templates/install.tmpl

@@ -99,7 +99,7 @@
 						<input id="domain" name="domain" value="{{.domain}}" placeholder="e.g. try.gitea.io" required>
 						<span class="help">{{.i18n.Tr "install.domain_helper"}}</span>
 					</div>
-					<div class="inline required field">
+					<div class="inline field">
 						<label for="ssh_port">{{.i18n.Tr "install.ssh_port"}}</label>
 						<input id="ssh_port" name="ssh_port" value="{{.ssh_port}}">
 						<span class="help">{{.i18n.Tr "install.ssh_port_helper"}}</span>