Remove needless reloading of each CachedCookbook on every resolve

For most actions, this turns an O(n^2) situation into O(n). Because
we're not needing to reload the cookbooks every time, Celluloid also
becomes unnecessary and we can remove that dependency, simplifying
a few more things.

Given a Berksfile containing all 107 cookbooks from the original
opscode repo (https://github.com/opscode/cookbooks/tree/0.10.rc.0)
and a warmup run to cache the cookbooks locally in ~/.berksfile, the
difference is striking:

Before fix (v2.0.9):

    ~/Code/berks-perf-test $ berks install
      ...
    ~/Code/berks-perf-test $ time berks install
      ...
    real  0m22.425s
    user  0m19.823s
    sys 0m3.673s

After fix (this commit):

    ~/Code/berks-perf-test $ berks install
      ...
    ~/Code/berks-perf-test $ time berks install
      ...
    real  0m3.527s
    user  0m2.892s
    sys 0m0.584s

Signed-off-by: Evan Owen <kainosnoema@gmail.com>