person-select: clean up translations

packages/person-select/src/i18n/de/translation.json

 {
   "person-select": {
     "placeholder": "Bitte wählen Sie eine Person aus",
-    "error-summary": "Ein Fehler ist aufgetreten",
     "login-required": "Anmeldung erforderlich"
   }
 }

packages/person-select/src/i18n/en/translation.json

 {
   "person-select": {
     "placeholder": "Please select a person",
-    "error-summary": "An error occurred",
     "login-required": "Login required"
   }
 }

packages/person-select/src/person-select.js

@@ -157,7 +157,7 @@ export class PersonSelect extends ScopedElementsMixin(AdapterLitElement) {
             width: '100%',
             language: this.lang === "de" ? select2LangDe() : select2LangEn(),
             minimumInputLength: 2,
-            placeholder: i18n.t(this.authenticated() ? 'person-select.placeholder' : 'person-select.login-required'),
+            placeholder: this.authenticated() ? i18n.t('person-select.placeholder') : i18n.t('person-select.login-required'),
             dropdownParent: this.$('#person-select-dropdown'),
             ajax: {
                 delay: 500,