chore: remove no longer used imports

Author: web-padawan

src/main/java/com/vaadin/demo/component/datepicker/DatePickerIndividualInputFields.java

@@ -14,7 +14,6 @@
 
 import java.time.LocalDate;
 import java.time.Month;
-import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 
 @Route("date-picker-individual-input-fields")

src/main/java/com/vaadin/demo/component/grid/GridHeaderFooterStyling.java

@@ -7,7 +7,6 @@
 import com.vaadin.flow.router.Route;
 
 import java.util.List;
-import java.util.stream.Collectors;
 
 @Route("grid-header-footer-styling")
 public class GridHeaderFooterStyling extends Div {

src/main/java/com/vaadin/demo/component/grid/GridStyling.java

@@ -7,7 +7,6 @@
 import com.vaadin.flow.router.Route;
 
 import java.util.List;
-import java.util.stream.Collectors;
 
 @Route("grid-styling")
 public class GridStyling extends Div {

src/main/java/com/vaadin/demo/fusion/security/authentication/UserInfoService.java

@@ -8,7 +8,6 @@
 import org.springframework.security.core.context.SecurityContextHolder;
 
 import java.util.List;
-import java.util.stream.Collectors;
 
 /**
  * Provides information about the current user.