$ lxc launch ubuntu-daily:x
Creating faithful-bunny
Starting faithful-bunny             
$ lxc exec faithful-bunny bash
root@faithful-bunny:~# apt purge initramfs-tools
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  apparmor* cloud-initramfs-copymods* cloud-initramfs-dyn-netconf*
  console-setup* console-setup-linux* cryptsetup* initramfs-tools* kbd*
  liblxc1* lxc-common* lxd* mdadm* overlayroot* plymouth*
  plymouth-theme-ubuntu-text* snapd* ubuntu-core-launcher* ubuntu-minimal*
0 upgraded, 0 newly installed, 18 to remove and 0 not upgraded.
After this operation, 86.8 MB disk space will be freed.
Do you want to continue? [Y/n] n
Abort.
# apt-add-repository 'deb http://archive.ubuntu.com/ubuntu xenial-proposed main'
# apt update
[...]
# apt install apparmor
[...]
# apt-add-repository -r 'deb http://archive.ubuntu.com/ubuntu xenial-proposed main'
# apt update
[...]
# apt purge initramfs-tools 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  binutils build-essential cpp cpp-5 dpkg-dev fakeroot g++ g++-5 gcc gcc-5
  libalgorithm-diff-perl libalgorithm-diff-xs-perl libalgorithm-merge-perl
  libasan2 libatomic1 libc-dev-bin libc6-dev libcc1-0 libcilkrts5 libdpkg-perl
  libfakeroot libfile-fcntllock-perl libgcc-5-dev libgomp1 libisl15 libitm1
  liblsan0 libmpc3 libmpx0 libquadmath0 libstdc++-5-dev libtsan0 libubsan0
  linux-libc-dev make manpages-dev
Suggested packages:
  binutils-doc cpp-doc gcc-5-locales debian-keyring g++-multilib
  g++-5-multilib gcc-5-doc libstdc++6-5-dbg gcc-multilib autoconf automake
  libtool flex bison gdb gcc-doc gcc-5-multilib libgcc1-dbg libgomp1-dbg
  libitm1-dbg libatomic1-dbg libasan2-dbg liblsan0-dbg libtsan0-dbg
  libubsan0-dbg libcilkrts5-dbg libmpx0-dbg libquadmath0-dbg glibc-doc
  libstdc++-5-doc make-doc
The following packages will be REMOVED:
  cloud-initramfs-copymods* cloud-initramfs-dyn-netconf* console-setup*
  console-setup-linux* cryptsetup* initramfs-tools* kbd* mdadm* overlayroot*
  plymouth* plymouth-theme-ubuntu-text* ubuntu-minimal*
The following NEW packages will be installed:
  binutils build-essential cpp cpp-5 dpkg-dev fakeroot g++ g++-5 gcc gcc-5
  libalgorithm-diff-perl libalgorithm-diff-xs-perl libalgorithm-merge-perl
  libasan2 libatomic1 libc-dev-bin libc6-dev libcc1-0 libcilkrts5 libdpkg-perl
  libfakeroot libfile-fcntllock-perl libgcc-5-dev libgomp1 libisl15 libitm1
  liblsan0 libmpc3 libmpx0 libquadmath0 libstdc++-5-dev libtsan0 libubsan0
  linux-libc-dev make manpages-dev
0 upgraded, 36 newly installed, 12 to remove and 0 not upgraded.
Need to get 38.3 MB of archives.
After this operation, 138 MB of additional disk space will be used.
Do you want to continue? [Y/n] 
#

It's unclear to me why removing initramfs-tools wants to add all of these other packages, but I don't think that's anything to do with the apparmor SRU; and I can get a clean removal with no new packages installed by running

# apt purge build-essential binutils make-guile cpp make libdpkg-perl initramfs-tools 

So I consider this v-done.