RFR(XXS) 8198287: Cleanup ElfFile usage in whitebox.cpp

[Zhengyu Gu]

elfFile.hpp is included twice in whitebox.cpp file.

The original one is included under LINUX guard for
WB_CheckLibSpecifiesNoexecstack test, which is only valid on Linux 
platform.

JDK-8193373 [1] added additional test for all supported platforms, which 
includes LINUX, so above instance should be removed.


Bug: http://cr.openjdk.java.net/~zgu/8198287/webrev.00/
Webrev: http://cr.openjdk.java.net/~zgu/8198287/webrev.00/


[1] https://bugs.openjdk.java.net/browse/JDK-8193373


Test:
   test-hotspot-gtest on Linux 64 (fastdebug and release)


Thanks,

-Zhengyu