Clean up unused SCSS in SMS message component

Things we don’t do with SMS messages any more:
- put paragraphs in them (we use `<br>` tags instead, to allow for
  multiple linebreaks)
- pick them using radio buttons
- render the template’s name as part of the template
- render the phone number that the message will be sent from as part of
  the template

app/assets/stylesheets/components/sms-message.scss

@@ -1,4 +1,3 @@
-%sms-message-wrapper,
 .sms-message-wrapper {
 
   width: 100%;
@@ -13,21 +12,6 @@
   clear: both;
   word-wrap: break-word;
 
-  p {
-    margin: 0;
-    line-height: 1.6;
-  }
-
-  p + p {
-    margin-top: 20px;
-  }
-
-}
-
-.sms-message-wrapper-with-radio {
-  @extend %sms-message-wrapper;
-  padding-left: 45px;
-  cursor: pointer;
 }
 
 .sms-message-recipient {
@@ -35,22 +19,3 @@
   color: $secondary-text-colour;
   margin: 10px 0 0 0;
 }
-
-.sms-message-name {
-  @include bold-24;
-  margin: 20px 0 5px 0;
-}
-
-.sms-message-picker {
-  display: block;
-  margin: 7px 0 0 0;
-  position: absolute;
-  left: 15px;
-  top: 50%;
-  z-index: 50;
-}
-
-.sms-message-from {
-  @include bold-19;
-  display: block;
-}