[bilibili] Remove copyrighted test cases

I can't find any English or Chinese material that claims BiliBili has
bought legal redistribution permissions for copyrighted products from
copyrighted holders.

References for removed test cases:
"刀语": https://en.wikipedia.org/wiki/Katanagatari, by White Fox
"哆啦A梦": https://en.wikipedia.org/wiki/Doraemon, by Shin-Ei Animation
"岳父岳母真难当": https://en.wikipedia.org/wiki/Serial_(Bad)_Weddings, by Les films du 24
"混沌武士": https://en.wikipedia.org/wiki/Samurai_Champloo, by Manglobe

I shouldn't have added them to _TESTS