Makefile: rm .install.libseccomp.sudo target

This was originally added in commit a824186 to be used from
Travis CI. Travis was removed in commit 8771a03 and there is
no need to have this target ever since (October 2018).

Also, remove the comment about BUILD_TAGS, which originally belonged to
varlink target (removed by commit f62a356) but got misplaced
later.

Signed-off-by: Kir Kolyshkin <[email protected]>

Makefile

@@ -887,13 +887,6 @@ install.tools: .install.ginkgo .install.golangci-lint .install.bats ## Install n
 		python3 -m pip install --user pre-commit; \
 	fi
 
-# $BUILD_TAGS variable is used in hack/golangci-lint.sh
-.PHONY: install.libseccomp.sudo
-install.libseccomp.sudo:
-	rm -rf ../../seccomp/libseccomp
-	git clone https://github.com/seccomp/libseccomp ../../seccomp/libseccomp
-	cd ../../seccomp/libseccomp && git checkout --detach $(LIBSECCOMP_COMMIT) && ./autogen.sh && ./configure --prefix=/usr && make all && make install
-
 .PHONY: uninstall
 uninstall:
 	for i in $(filter %.1,$(MANPAGES_DEST)); do \