lib/Makefile: remove CONFIG_AVERAGE build rule

The Kconfig option AVERAGE and its implementation has been removed by
commit f4e774f55fe0 ("average: remove out-of-line implementation").
Remove the dead build rule in lib/Makefile.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/Makefile

@@ -138,8 +138,6 @@ obj-$(CONFIG_GENERIC_ATOMIC64) += atomic64.o
 
 obj-$(CONFIG_ATOMIC64_SELFTEST) += atomic64_test.o
 
-obj-$(CONFIG_AVERAGE) += average.o
-
 obj-$(CONFIG_CPU_RMAP) += cpu_rmap.o
 
 obj-$(CONFIG_CORDIC) += cordic.o