Bugfix - commenting-out unused member which results in build error on OS X with latest Xcode.

- Build error due to -Werror,-Wunused-private-field clang args.
- Raised with gtest group (as it also occurs with latest gtest:master but for a different
  variable) with patch, but they don't want to fix for compatibility with legacy compilers/OS
  see here: https://groups.google.com/forum/?fromgroups=#!topic/googletestframework/S1KLl2jkzws

Change-Id: I99984bcd9d07f6eb0e3fac58e27ddf0ac9e54265