Internationalize SMS placeholder input (#1218)

Turns out the library does this - we just needed to remove our
placeholder...

cmd/server/assets/codes/issue.html

@@ -139,7 +139,7 @@ <h1>{{t $.locale "header.create-verification-code"}}</h1>
               <label for="symptomDate" class="col-sm-3">Patient phone</label>
               <div class="col-sm-9">
                 <div class="input-group">
-                  <input type="tel" id="phone" name="phone" class="form-control" placeholder="+1 (555) 555-5555" autocomplete="off" class="w-100" />
+                  <input type="tel" id="phone" name="phone" class="form-control" autocomplete="off" class="w-100" />
                 </div>
                 <small class="form-text text-muted">
                   If provided, the system will send text containing the code to the