staging:iio:gyro: Remove stale Makefile entry

Commit a301d425e ("staging:iio:gyro remove adis16251 driver as now supported by
adis16260 driver") removed the adis16251, but left its Makefile entry intact.
This patch removes the unused Makefile entry.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
diff --git a/drivers/staging/iio/gyro/Makefile b/drivers/staging/iio/gyro/Makefile
index 1303569..79bef4e 100644
--- a/drivers/staging/iio/gyro/Makefile
+++ b/drivers/staging/iio/gyro/Makefile
@@ -14,8 +14,5 @@
 adis16260-y             := adis16260_core.o
 obj-$(CONFIG_ADIS16260) += adis16260.o
 
-adis16251-y             := adis16251_core.o
-obj-$(CONFIG_ADIS16251) += adis16251.o
-
 adxrs450-y             := adxrs450_core.o
 obj-$(CONFIG_ADXRS450) += adxrs450.o