base/i18n: Remove unneeded includes in case_conversion.*

These includes are not needed anymore since r84855.

BUG=None
TEST=None

R=evan@chromium.org

Review URL: http://codereview.chromium.org/7032008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@85559 0039d316-1c4b-4281-b951-d872f2087c98
string16 ToUpper(const string16& string) {
  icu::UnicodeString unicode_string(string.c_str(), string.size());
  unicode_string.toUpper();
  return string16(unicode_string.getBuffer(), unicode_string.length());
}

string16 ToUpper(const string16& string) {
  icu::UnicodeString unicode_string(string.c_str(), string.size());
  unicode_string.toUpper();
  return string16(unicode_string.getBuffer(), unicode_string.length());
}
