symbols/macintosh_vndr/jp: Drop a workaround for old Mozc
Mozc build 4780 includes a change that allows to recognize the symbols Hangul
and Hangul_Hanja
as ImeOn and ImeOff:
https://github.com/google/mozc/commit/80bc73f06dcd4e1a52a03f46c2ae308f3e1bddb6
The workaround introduced with commit be506a88 is now obsolete and removed.
Edited by 小田喜陽彦