Move ICU header part 2

Move ICU header part 2

Move public/i18n/unicode to source/i18n/unicode, delete public/{common,i18n}.
Update icu.gyp accordingly.

This move is done in stages to work around a problem with gcl handling a
large patch. 

All-in-one patch was approved at https://codereview.chromium.org/18836004/

The upstream has headers in source/{common,i18n}/unicode. 
With Blink's ICU headers removed, there's no need to keep them 
in a location different than the upstream. Future ICU updates will 
be a bit more streamlined. v8 also likes to have this change. 

The Chrome-side of change is at http://codereview.chromium.org/18252003 

This revision will be rolled in along with the global replacements 
of include-references to ICU headers and DEPS changes. 

See also http://crbug.com/232922 where ICU headers in Blink are removed. 

BUG=251433
TEST=NONE for now.
TBR=mark,cpu

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=211848

[jungshik at Google, 2013-07-16 21:23:19]

Committed patchset #2 manually as r211848 (presubmit successful).