RFR: 8033565: Remove unused nativeNewStringPlatform and nativeGetStringPlatformChars

[roger riggs]

Please review this change to remove unused support in jni_util.c for
functions nativeNewStringPlatform and nativeGetStringPlatformChars.

On Windows, both were conditional on jvm.dll being installed on a path 
containing "kernel".
On Solaris, Linux, and Mac, they had no-op implementations.

Webrev:
http://cr.openjdk.java.net/~rriggs/webrev-remove-nativenewstring-8033565/

Thanks, Roger