wstring: remove wstring version of SplitString

Retry of r84336.

BUG=23581

Review URL: http://codereview.chromium.org/6930047

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@84355 0039d316-1c4b-4281-b951-d872f2087c98
void Label::SetTooltipText(const std::wstring& tooltip_text) {
  tooltip_text_ = WideToUTF16Hack(tooltip_text);
}

void Label::SetTooltipText(const std::wstring& tooltip_text) {
  tooltip_text_ = WideToUTF16Hack(tooltip_text);
}
