Don't purge busybox-static in minimized, no longer installed

This caused the builds to fail because we were purging are non
existing package.

debian/changelog

@@ -1,3 +1,9 @@
+livecd-rootfs (2.582) UNRELEASED; urgency=medium
+
+  * Don't purge busybox-static in minimized, no longer installed
+
+ -- Julian Andres Klode <juliank@ubuntu.com>  Mon, 13 May 2019 14:22:38 +0200
+
 livecd-rootfs (2.581) eoan; urgency=medium
 
   * Remove device nodes later for ubuntu-base:minimized (i.e. docker) builds.

live-build/auto/build

@@ -293,7 +293,7 @@ EOF
 			# would only be seen by humans
 			Chroot chroot "env DEBIAN_FRONTEND=noninteractive \
 				apt-get -y purge initramfs-tools busybox-initramfs \
-					busybox-static landscape-common"
+					landscape-common"
 			# and if initramfs-tools was configured before our kernel,
 			# /etc/kernel/postinst.d/initramfs-tools will have created
 			# an initramfs despite the generic dpkg-divert; so remove it