powerpc: mpc8xx: remove stxxtc board support

This board has been orphaned for a while and old enough.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/include/common.h b/include/common.h
index 1d6cb48..c7e51ca 100644
--- a/include/common.h
+++ b/include/common.h
@@ -32,10 +32,7 @@
     defined(CONFIG_MPC866)	|| \
     defined(CONFIG_MPC866P)
 # define CONFIG_MPC866_FAMILY 1
-#elif defined(CONFIG_MPC870) \
-   || defined(CONFIG_MPC875) \
-   || defined(CONFIG_MPC880) \
-   || defined(CONFIG_MPC885)
+#elif defined(CONFIG_MPC885)
 # define CONFIG_MPC885_FAMILY   1
 #endif
 #if   defined(CONFIG_MPC860)	   \