refactor: remove some unused SCSS

I searched the codebase and it appears to not have these classes.

The majority of the elements that use the removed classes
were removed in e04604a,
then `import-qr-code-dialog` was removed, in e2b23d3.

e6f0521 introduced
`ephermeral-message__select-option` SCSS, but no elements use it.
`git log -S"ephemeral-message"` shows only this commit.

packages/frontend/scss/_variables.scss

@@ -31,7 +31,6 @@ $z-index: (
   // ============
   chatlist-scope-floating-action-button: 1,
   jump-down-button-scope-counter: 1,
-  import-qr-code-dialog-scope-scan-qr-description: 1,
   account-list-sidebar-scope-account-badge: 1,
 
   // Global Scope

packages/frontend/scss/dialogs/_autocrypt_setup.scss

@@ -48,16 +48,3 @@
     }
   }
 }
-
-.enter-autocrypt-setup-message-dialog {
-  .dialog-body {
-    padding: 0px 10px;
-    background: var(--bgPrimary);
-  }
-
-  p.autocrypt-setup-error {
-    background-color: rgba(255, 0, 0, 0.2);
-    padding: 5px 6px;
-    white-space: pre-wrap;
-  }
-}

packages/frontend/scss/dialogs/_settings.scss

@@ -62,25 +62,6 @@
     align-items: center;
     flex-direction: column;
   }
-  .profile-displayname-addr {
-    display: flex;
-    margin-left: 20px;
-    flex-direction: column;
-    justify-content: center;
-
-    .displayname {
-      font-size: large;
-      font-weight: 200;
-    }
-
-    .addr {
-      color: #969696;
-      margin-top: 5px;
-      text-overflow: ellipsis;
-      overflow-wrap: break-word;
-      overflow-wrap: anywhere;
-    }
-  }
 }
 
 .theme-meta {

packages/frontend/scss/manifest.scss

@@ -37,10 +37,7 @@
 @import 'dialogs/_settings';
 @import 'dialogs/_view_profile';
 @import 'dialogs/_mailto-dialog';
-@import 'dialogs/_qr-import';
-@import 'dialogs/_ephermeral_message';
 @import 'dialogs/_qr-code';
-@import 'dialogs/multidevice/send_backup';
 @import 'dialogs/webxdc_send_to_chat.scss';
 
 // Login