Comment 1 for bug 1376809

The package is optional because it is not required on a VM for instance. If you read the output of the apt-get remove crda command you will notice it is proposing to remove the larger part of your kernel (linux-image-extra) which contains all of your hardware drivers, and explains the panic on next boot:

  $ sudo apt-get remove crda
  [sudo] password for mru:
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  The following extra packages will be installed:
    crda:i386 gcc-4.9-base:i386 libc6:i386 libgcc1:i386 libnl-3-200:i386
    libnl-genl-3-200:i386 libssl1.0.0:i386 wireless-crda
  Suggested packages:
    glibc-doc:i386 locales:i386
  The following packages will be REMOVED
    crda linux-generic linux-image-extra-3.13.0-36-generic linux-image-generic
  The following NEW packages will be installed
    crda:i386 gcc-4.9-base:i386 libc6:i386 libgcc1:i386 libnl-3-200:i386
    libnl-genl-3-200:i386 libssl1.0.0:i386 wireless-crda
  0 to upgrade, 8 to newly install, 4 to remove and 0 not to upgrade.
  Need to get 4,922 kB of archives.
  After this operation, 139 MB disk space will be freed.
  Do you want to continue? [Y/n] n
  $

If you have an older kernel installed you should be able to boot into grub (hold shift during very early boot) and select the older kernel. From there you should be able reinstall the kernel "apt-get install linux-image-generic".