Remove WTF_LOG_VERBOSE macro

Remove WTF_LOG_VERBOSE macro as was suggested at https://codereview.chromium.org/95303002/, since this macro is not used anywhere.

Review URL: https://codereview.chromium.org/108043003

git-svn-id: svn://svn.chromium.org/blink/trunk@163370 bbb929c8-8fbe-4397-9dbb-9b2b20218538