Makefile: remove redundant BUILDFLAGS

We don't set it, so there's no need to keep it.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

Makefile

@@ -22,7 +22,6 @@ ETCDIR ?= /etc
 TMPFILESDIR ?= ${PREFIX}/lib/tmpfiles.d
 SYSTEMDDIR ?= ${PREFIX}/lib/systemd/system
 USERSYSTEMDDIR ?= ${PREFIX}/lib/systemd/user
-BUILDFLAGS ?=
 BUILDTAGS ?= \
 	$(shell hack/apparmor_tag.sh) \
 	$(shell hack/btrfs_installed_tag.sh) \