feedback: move feedback code to the single file

Feedback daemon's code was located in two files:
box/lua/feedback_daemon.lua and box/lua/schema.lua. That makes
it harder to eliminate the daemon at cmake configuration time.

Now all its code is in one place, in feedback_daemon.lua. Disable
of the daemon's code now is a matter of excluding the Lua file
from source code.

Part of #3308