ipc_fuzzer: comment out #endif comment.

Needed to cure this build error:
../../tools/ipc_fuzzer/mutate/rand_util.h:40:8: error: extra tokens at end of #endif directive [-Werror,-Wextra-tokens]

Review URL: https://codereview.chromium.org/150633007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248203 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248203