refactor: remove deprecated lastName field from user settings

- Remove lastName field from $saveUserSettings and $saveSettings calls
- Clean up deprecated pre v0.1.3 code

src/views/NewEditAccountView.vue

@@ -118,13 +118,11 @@ export default class NewEditAccountView extends Vue {
       // Save to user-specific settings for the current identity
       await this.$saveUserSettings(activeDid, {
         firstName: this.givenName,
-        lastName: "", // deprecated, pre v 0.1.3
       });
     } else {
       // Fallback to master settings if no active DID
       await this.$saveSettings({
         firstName: this.givenName,
-        lastName: "", // deprecated, pre v 0.1.3
       });
     }