Delete three pre-built assembly source files because they're now
generated at build-time.

Update data build scripts and README.chromium accordingly.

Update copy_data.sh and copy_data_android.sh so that the assembly
source files are not copied. Besides, convert the little endian
data bundle to the big endian data bundle for non-Android platforms.

BUG=v8:4828
TEST=Rebuild icu data following the procedure in README.chromium
TEST='gn args <builddir>' with icu_use_data_file set to true or false
TEST=build base_unittests and run with --gtest_filter=ICU*
TEST=build base_unittests and run with --gtest_filter=Message*ormat*
TEST=build 'd8' (v8) and try `(new Date()).toLocaleString("de")`

Review URL: https://codereview.chromium.org/2182883004 .

* Update the pre-built ICU data files for all platforms

  source/data/in/icudtl.dat for non-Android platforms
  {linux,mac}/icudt*.S for linux/mac
  android/icudtl.dat and android/icudt*.S for Android
  windows/icudt.dll for Windows

* Update Android data trimming script

  1. Make sure that 'default' calendar is kept in locales where it's relevant
    : root, th, fa, ar_SA, etc.
  2. Add a minimal region data to work around a bug in ICU with pool.res
     handling

* Update gn and gyp files
* And add a TODO comment to update.sh to automate the build file update.
* Add it_CH to the locale list.
* Add sr_Latn to unit/reslocal.mk (required by sh) and
  line_normal_fi to brkitr/brklocal.mk (referred to in brkitr/fi.txt) in
  place of line_fi.

* Update and add scripts for data building
* Completely rewrite README.chromium
* Check-in the prebuilt ICU data files/assembly sources for
  Linux,Mac,Windows,Chrome OS and Android.

BUG=575007
TEST=Blink layout tests, webkit unittests
TEST=All bots can build successfully
TEST=net_unittests --gtest_filter="*ilenameUtil*"
TEST=net_unittests --gtest_filter="*IDN*" (pending bug 336973)
TEST=base_unittests --gtest_filter="*Conv*"
TEST=browser_tests --gtest_filter="*ncoding*"
TEST=base_unittests --gtest_filter="*essage*"
TEST=ui_base_unittests --gtest_filter="*ormat*"
TEST=ui_base_unittests --gtest_filter="L10n*"
R=mark@chromium.org

Review URL: https://codereview.chromium.org/1639543006 .