Always enable SPLASH_CMYK

Doesn't seem to cause any speed regression and one ifdef less is code easier
to maintain
6 jobs for always_splash_cmyk in 5 minutes and 7 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #526761
build

00:02:45

passed #526766
build_android

00:00:56

passed #526762
build_clang_libcpp

00:03:01

passed #526765
build_clazy

00:05:04

passed #526764
build_mingw64_fedora

00:03:16

passed #526763
build_ubuntu_16_04

00:01:34