Revert "package/collectd: disable libupsclient"

This reverts commit 0be1c3e921036ff870b6d60c0d55ceac81367c3c.

The actual issue is more complex. The problem purportedly fixed was not
caused by a missing libupsclient (it was present), but by a missing type
definition for time_t (on a musl toolchain).

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/collectd/collectd.mk

@@ -45,7 +45,6 @@ COLLECTD_CONF_OPTS += \
 	--with-nan-emulation \
 	--with-fp-layout=$(COLLECTD_FP_LAYOUT) \
 	--with-perl-bindings=no \
-	--without-libupsclient \
 	--disable-werror \
 	$(foreach p, $(COLLECTD_PLUGINS_DISABLE), --disable-$(p)) \
 	$(if $(BR2_PACKAGE_COLLECTD_AGGREGATION),--enable-aggregation,--disable-aggregation) \