[9] Review Request: 8072665 SoundLibraries.gmk and SoundDefs.h: remove isSigned8() dead code

[Sergey Bylokhov]

Hello.
Please review a fix for jdk 9.
Unused method was removed. See additional information in bug description.

Bug: https://bugs.openjdk.java.net/browse/JDK-8072665
Webrev can be found at: http://cr.openjdk.java.net/~serb/8072665/webrev.00

--
Best regards, Sergey.