Removed unused import

See: https://github.com/cryptomator/cryptomator/pull/2996#discussion_r1263556873

src/main/java/org/cryptomator/common/mount/MountWithinParentUtil.java

@@ -4,7 +4,6 @@ import org.apache.commons.lang3.SystemUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.nio.file.DirectoryNotEmptyException;
 import java.nio.file.FileAlreadyExistsException;