CLEANUP: hlua: fix conflicting comment in hlua_ctx_destroy()

CLEANUP: hlua: fix conflicting comment in hlua_ctx_destroy()

The comment for the hlua_ctx_destroy() function states that the "lua"
struct is not freed.

This is not true anymore since 2c8b54e7 ("MEDIUM: lua: remove Lua struct
from session, and allocate it with memory pools")

Updating the function comment to properly report the actual behavior.

This could be backported in every stable versions with 2c8b54e7
("MEDIUM: lua: remove Lua struct from session, and allocate it with memory pools")