remove serialization. it's moved to github

remove serialization. it's moved to github

BUG=
R=alanknight@google.com

Committed: https://code.google.com/p/dart/source/detail?r=40447

[sethladd, 2014-09-15 21:36:12]

sethladd@google.com changed reviewers:
+ alanknight@google.com

[sethladd, 2014-09-17 16:52:27]

Friendly ping

[Alan Knight, 2014-09-17 16:56:12]

Was just going to write you an email. So I have the changes to not import
mirrors in the main serialization library in the main repo. Would it be easier
to submit that first and then copy the change over to github before deleting, or
to patch it out of there into github first?

[sethladd, 2014-09-17 20:26:39]

In the meantime, how does this look? Did I cover all the mentions of the
serialization package?

[Alan Knight, 2014-09-18 17:57:53]

lgtm

[sethladd, 2014-09-18 17:59:21]

Committed patchset #1 (id:1) manually as 40447 (presubmit successful).