feat(sms): remove SMS padlock

Fixes #6653

app/images/icon-secure-lock.svg

@@ -1,4 +0,0 @@
-<!-- This Source Code Form is subject to the terms of the Mozilla Public
-   - License, v. 2.0. If a copy of the MPL was not distributed with this
-   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
-<svg width="20" height="20" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" clip-rule="evenodd" d="M9 7a3 3 0 1 1 6 0v3H9V7zm-2 3V7a5 5 0 1 1 10 0v3h1a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2v-8a2 2 0 0 1 2-2h1z" fill="#FFFFFF" fill-opacity="1"></path></svg>

app/scripts/templates/sms_send.mustache

@@ -18,7 +18,7 @@
       <form novalidate>
         <div class="input-row sms-row">
           <input name="phoneNumber" class="phone-number" type="tel" data-country="{{country}}" value="{{phoneNumber}}" placeholder="{{#t}}Mobile phone number{{/t}}" required autofocus="autofocus" />
-          <button type="submit" class="sms-send primary-button"><span class="sms-send-lock"></span>{{#t}}Send{{/t}}</button>
+          <button type="submit" class="sms-send primary-button">{{#t}}Send{{/t}}</button>
         </div>
       </form>
     </section>

app/styles/modules/_branding.scss

@@ -109,13 +109,6 @@
     width: auto;
     z-index: 3;
 
-    .sms-send-lock {
-      background: image-url('icon-secure-lock.svg') no-repeat 0 2px;
-      display: block;
-      height: 20px;
-      width: 20px;
-    }
-
     html[dir='ltr'] & {
       border-left: 1px solid $input-border-color-default;
       right: 1px;