Implemented the default functionality of user combobox.

Author: KarnaiahPesula

sormas-ui/src/main/java/de/symeda/sormas/ui/utils/UserField.java

@@ -44,8 +44,6 @@ protected Component initContent() {
 		userCombo = ComboBoxHelper.createComboBoxV7();
 		userCombo.addItems(items);
 
-		userCombo.setNewItemsAllowed(true);
-
 		userCombo.setImmediate(true);
 		if (getValue() != null) {
 			userCombo.addItem(getValue());