Remove remaining fontawesome usage in templates (#15952)

Can not remove the dependency yet because easymde depends on it.

templates/user/auth/signin_navbar.tmpl

@@ -6,13 +6,13 @@
 		</a>
 		{{if .EnableOpenIDSignIn}}
 		<a class="{{if .PageIsLoginOpenID}}active{{end}} item" rel="nofollow" href="{{AppSubUrl}}/user/login/openid">
-			<i class="fa fa-openid"></i>
+			{{svg "fontawesome-openid"}}
 			&nbsp;OpenID
 		</a>
 		{{end}}
 		{{if .EnableSSPI}}
 		<a class="item" rel="nofollow" href="{{AppSubUrl}}/user/login?auth_with_sspi=1">
-			<i class="fa fa-windows"></i>
+			{{svg "fontawesome-windows"}}
 			&nbsp;SSPI
 		</a>
 		{{end}}

templates/user/auth/signin_openid.tmpl

@@ -4,7 +4,7 @@
 	<div class="ui container">
 		{{template "base/alert" .}}
 		<h4 class="ui top attached header center">
-			<i class="fa fa-openid"></i>
+			{{svg "fontawesome-openid"}}
 			OpenID
 		</h4>
 		<div class="ui attached segment">
@@ -15,7 +15,7 @@
 			</div>
 			<div class="required inline field {{if .Err_OpenID}}error{{end}}">
 				<label for="openid">
-				<i class="fa fa-openid"></i>
+				{{svg "fontawesome-openid"}}
 				OpenID URI
 				</label>
 				<input id="openid" name="openid" value="{{.openid}}" autofocus required>