Fix checkstyle

Signed-off-by: Vasily Pelikh <2010720+vpelikh@users.noreply.github.com>

Author: vpelikh

native-gradle-plugin/src/main/java/org/graalvm/buildtools/gradle/internal/DefaultGraalVmExtension.java

@@ -61,8 +61,6 @@
 import javax.inject.Inject;
 import java.util.function.Predicate;
 
-import java.io.File;
-
 public abstract class DefaultGraalVmExtension implements GraalVMExtension {
     private final transient NamedDomainObjectContainer<NativeImageOptions> nativeImages;
     private final transient NativeImagePlugin plugin;