RFR: JDK-8161601 Solaris: __USE_LEGACY_PROTOTYPES__ is redundant and should be removed

[Alan Burlison]

David Holmes pointed out to me that there were instances of 
__USE_LEGACY_PROTOTYPES__ in Solaris-related code that were redundant, 
this patch removes them.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8161601

Webrev:
http://sthjprt.uk.oracle.com/archives/2016/07

All JPRT tests were successful.

-- 
Alan Burlison
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