styles: Unprefix appearance property.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/styles/portico/billing.scss

@@ -275,9 +275,9 @@
 
 input[type="number"]::-webkit-outer-spin-button,
 input[type="number"]::-webkit-inner-spin-button {
-    -webkit-appearance: none;
+    appearance: none;
     margin: 0;
 }
 input[type="number"] {
-    -moz-appearance: textfield;
+    appearance: textfield;
 }

static/styles/settings.scss

@@ -1655,7 +1655,7 @@ body:not(.night-mode) #settings_page .custom_user_field .datepicker {
 
 @supports (-moz-appearance: none) {
     #settings_page select {
-        -moz-appearance: none;
+        appearance: none;
         background: hsl(0, 0%, 100%) url(../images/dropdown.png) right / 20px
             no-repeat;
         padding-right: 20px;