remove extra method="get" from device-code template (#4145)

In device-code template, same form tag has method="post", then
followed by method="get".. Chrome can handle that as post just fine,
but in headless environments you might be using Lynx, which uses GET:
it results in 400 Bad Request from Dex server.

Signed-off-by: Tuomo Tanskanen <tuomo.tanskanen@est.tech>

web/templates/device.html

@@ -2,7 +2,7 @@
 
 <div class="theme-panel">
   <h2 class="theme-heading">Enter User Code</h2>
-  <form method="post" action="{{ .PostURL }}" method="get">
+  <form method="post" action="{{ .PostURL }}">
     <div class="theme-form-row">
       {{ if( .UserCode  )}}
       <input tabindex="2" required id="user_code" name="user_code" type="text" class="theme-form-input" autocomplete="off" value="{{.UserCode}}" {{ if .Invalid }} autofocus {{ end }}/>