remove unused imports

Author: robaho

src/main/java/robaho/net/httpserver/ExchangeImpl.java

@@ -35,12 +35,8 @@
 import java.lang.System.Logger.Level;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
-import java.time.Instant;
 import java.time.ZoneId;
-import java.time.ZoneOffset;
 import java.time.format.DateTimeFormatter;
-import java.time.format.TextStyle;
-import java.util.stream.Stream;
 
 import com.sun.net.httpserver.*;