topology: fix unused-const-variable warning

Last year, unused static const variable was added, then compiler generates
a below warning.

dapm.c:43:30: warning: ‘widget_control_map’ defined but not used [-Wunused-const-variable=]
 static const struct map_elem widget_control_map[] = {
                              ^~~~~~~~~~~~~~~~~~

This commit removes it.

Fixes: 01a0e1a1 ("topology: Add DAPM object parser")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>