Stop using fixpath -detach with javac server

In JDK-8143296, I introduced a -detach parameter to fixpath to fix a problem with javac server on Windows. This problem was related to our use of logger.sh for capturing compiler output into log files. Since then, in JDK-8146403, I got rid of logger.sh and use a different method of capturing output to files. The new method does not seem to interfere with the javac server process, so we can get rid of this rather pesky workaround.