Remove revert button for absent teachers

aleksis/apps/chronos/frontend/components/substitutions/SubstitutionCard.vue

@@ -43,9 +43,6 @@ import createOrPatchMixin from "aleksis.core/mixins/createOrPatchMixin.js";
             outlined
             color="error"
             class="mb-2"
-            close
-            close-icon="mdi-reload"
-            @click:close="addTeacher(teacher)"
           >
             <v-icon left> $cancel </v-icon>
             <div class="text-decoration-line-through">