EmacsList,Go,Lisp: use `Y` instead of `u` to represent unknown Language objects

[masatake]

EmacsLisp            u      unknown               yes     no      0      NONE   unknown type of definitions
Go                   u      unknown               yes     yes     1      NONE   unknown
Lisp                 u      unknown               yes     no      0      NONE   unknown type of definitions
Python               x      unknown               yes     no      2      NONE   name referring a class/variable/function/module defined in other module

Though breaking compatibilities, I will change the letters for unknown to Y.

Originally posted by @masatake in #3535 (comment)

[masatake]

Surprisingly, I solved this one in #3567.