JDK 9 RFR of 8162624: (fs) Remove FileTypeDetectors based on libgio and libmagic

[Brian Burkhalter]

Please review at your convenience.

Issue:	https://bugs.openjdk.java.net/browse/JDK-8162624
Patch:	http://cr.openjdk.java.net/~bpb/8162624/webrev.00/

Remove GioFileTypeDetector and MagicFileTypeDetector as these seem not to provide significant value, introduce unpredictability into the result of file probing, and are inconsistent with the other principle server side platform Solaris.

Thanks,

Brian