Roll ICU to c56c671

The reduces the ICU data file even more:

Uncompressed size: 883,280B (862.6 KB), minus 363.2KB
Compressed size: 460,972B (450.2KB), minus 83.9KB

The following unused resources are removed comapred to previous version:
 * uts46.nrm
 * nfkc_cf.nrm
 * cnvalias.icu
 * Break Iterators for:
   * Sentence breaks
   * Title breaks
   * CSS-specific line breaks ("regular" line breaks are still supported)

Author: goderbauer

DEPS

@@ -150,7 +150,7 @@ deps = {
    Var('chromium_git') + '/chromium/src/ios.git' + '@' + Var('ios_tools_revision'),
 
   'src/third_party/icu':
-   Var('chromium_git') + '/chromium/deps/icu.git' + '@' + '6cf2ab2580888e520683c2d993133018c91e612c',
+   Var('chromium_git') + '/chromium/deps/icu.git' + '@' + 'c56c671998902fcc4fc9ace88c83daa99f980793',
 
   'src/third_party/dart':
    Var('dart_git') + '/sdk.git' + '@' + Var('dart_revision'),