Remove SHELL_COLOR build flag

Now that mp_printf() no longer prints the CPU MPID at the beginning of
each string, the SHELL_COLOR build flag has no effect.

Change-Id: Ia70c46d21bae9d14ff1177a5dae18f1006d5eed1
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
3 files changed