common: Makefile: drop duplicated line

obj-$(CONFIG_$(SPL_TPL_)YMODEM_SUPPORT) += xyzModem.o is there,
no need obj-$(CONFIG_SPL_YMODEM_SUPPORT) += xyzModem.o

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>