Remove icu as a dependency

In https://codereview.webrtc.org/1430023005 all the code
references to ICU were removed. This actually removes the
library from being referenced.

TESTED=git cl try -c --bot=win_compile_rel --bot=linux_compile_rel --bot=android_compile_rel --bot=mac_compile_rel --bot=ios_rel -m tryserver.webrtc
R=phoglund@webrtc.org

Review URL: https://codereview.webrtc.org/1417563006 .

Cr-Commit-Position: refs/heads/master@{#10584}

.gitignore

@@ -94,7 +94,6 @@
 /third_party/gaeunit
 /third_party/gflags/src
 /third_party/google-visualization-python
-/third_party/icu
 /third_party/instrumented_libraries
 /third_party/ijar
 /third_party/jsoncpp

setup_links.py

@@ -40,7 +40,6 @@ DIRECTORIES = [
   'third_party/colorama',
   'third_party/drmemory',
   'third_party/expat',
-  'third_party/icu',
   'third_party/instrumented_libraries',
   'third_party/jsoncpp',
   'third_party/libjpeg',