sandbox: Drop the deprecated 'sb' command

The old 'sb' command was deprecated in 2015 and replaced with 'host'.
Remove the remaining users and the command, so that the name is available
for other purposes.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/sf.c b/test/dm/sf.c
index 35dce4e..3788d59 100644
--- a/test/dm/sf.c
+++ b/test/dm/sf.c
@@ -79,7 +79,7 @@
 	 * benefit is worth the extra complexity.
 	 */
 	ut_asserteq(0, run_command_list(
-		"sb save hostfs - 0 spi.bin 200000;"
+		"host save hostfs - 0 spi.bin 200000;"
 		"sf probe;"
 		"sf test 0 10000", -1,  0));
 	/*