RFR 8165889: Remove jdk.test.lib.unsafe.UnsafeHelper

[George Triantafillou]

Please review the following fix:

JBS: https://bugs.openjdk.java.net/browse/JDK-8165889

Open webrevs:
http://cr.openjdk.java.net/~gtriantafill/8165889/jdk.patch/webrev/
<http://cr.openjdk.java.net/%7Egtriantafill/8165889/jdk.patch/webrev/>http://cr.openjdk.java.net/~gtriantafill/8165889/jdk-test.patch/webrev/ 
<http://cr.openjdk.java.net/%7Egtriantafill/8165889/jdk-test.patch/webrev/>
http://cr.openjdk.java.net/~gtriantafill/8165889/hotspot-test.patch/webrev/
<http://cr.openjdk.java.net/%7Egtriantafill/8165889/hotspot-test.patch/webrev/>
Summary:
jdk.test.lib.unsafe.UnsafeHelper has been replaced by 
jdk.internal.misc.Unsafe. Tests using jdk.test.lib.unsafe.UnsafeHelper 
need to be updated to use jdk.internal.misc.Unsafe.

- Removed test/lib/jdk/test/lib/unsafe/UnsafeHelper.java
- Replaced uses of UnsafeHelper.getUnsafe() with Unsafe.getUnsafe()
- Removed unnecessary calls to setAccessible(true)

Tested locally on Linux.

Thanks.

-George