fix: address Checkstyle issues

Author: zikunz

src/main/java/org/jabref/gui/preferences/journals/AbbreviationsFileViewModel.java

@@ -4,12 +4,10 @@
 import java.nio.file.Files;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
-import java.util.stream.Collectors;
 
 import javafx.beans.property.BooleanProperty;
 import javafx.beans.property.ReadOnlyBooleanProperty;