Remove unused Mac platform code.

Most of ColorMac.h is unused (except for one function, which is only
used in one file, but seems general enough to remain).

EmptyProtocolDefinitions.h is included only in one source file, which
does not refer to either of the protocol definitions it provides.

Review URL: https://codereview.chromium.org/336523003

git-svn-id: svn://svn.chromium.org/blink/trunk@176094 bbb929c8-8fbe-4397-9dbb-9b2b20218538