Remove Backslash-as-JPY hack

We should not go to extra length to emulate 'the broken' behavior of Windows
Japanese fonts on non-Windows platforms.

BUG=305827
TEST=Layout test (related tests are removed).

Review URL: https://codereview.chromium.org/27030014

git-svn-id: svn://svn.chromium.org/blink/trunk@159589 bbb929c8-8fbe-4397-9dbb-9b2b20218538