Remove subfolders from Favorites

Signed-off-by: GretaD <gretadoci@gmail.com>

src/components/NavigationFolder.vue

@@ -51,7 +51,7 @@
 					{{ t('mail', 'Mark all messages of this folder as read') }}
 				</ActionButton>
 
-				<ActionInput v-if="!account.isUnified" icon="icon-add" @submit="createFolder">
+				<ActionInput v-if="!account.isUnified && folder.specialRole !== 'flagged'" icon="icon-add" @submit="createFolder">
 					{{ t('mail', 'Add subfolder') }}
 				</ActionInput>
 			</template>