Remove duplicates found in candidates of quick for cangjie 5

In cangjie 5, some words have 2 input method like:
hnhli  風
hnmli  風
eill   洲
emll   洲

Then two duplicated candidate will be formed in quick for cangjie5.

Bochecha said using set instead of vector would be good, but it might break the api (like no "push_back" in set)

So i think using that method will be a good choice for quick and safe implementation.