tcg/mips: Replace MIPS_BE with HOST_BIG_ENDIAN

Since e03b56863d2b, which replaced HOST_WORDS_BIGENDIAN
with HOST_BIG_ENDIAN, there is no need to define a second
symbol which is [0,1].

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>