package/pkg-cmake.mk: remove the USE_CCACHE CMake flag for host-package

The USE_CCACHE CMake flag is only useful when building target package
(only the toolchainfile.cmake uses it).

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>