Where did you see that? I'm skeptical of that claim because I know some embedded uses of Lua strongly utilize pre-compiling to Lua bytecode so they can keep their hardware as slim as possible. I know some will even strip out the Lua compiler from the binary they ship to shrink the profile even more. Also, many video games like to pre-compile their shipped Lua scripts to reduce their load times.
I know that the Lua team has internal private repositories, and that luac is developed in a separate repo for them. I've seen occasional reports on the Lua mailing list that luac.c is forgotten or not updated in non-official releases. That is because those source drops didn't go through the full official release process which includes merging in from their luac repo. Maybe you are confusing these intermediate source drops with deprecation? If there is deprecation, I would like to see the details on that. I presume they would be introducing some kind of replacement that addresses all the real world use cases that rely on the abilities of pre-compiling to Lua bytecode.
I know that the Lua team has internal private repositories, and that luac is developed in a separate repo for them. I've seen occasional reports on the Lua mailing list that luac.c is forgotten or not updated in non-official releases. That is because those source drops didn't go through the full official release process which includes merging in from their luac repo. Maybe you are confusing these intermediate source drops with deprecation? If there is deprecation, I would like to see the details on that. I presume they would be introducing some kind of replacement that addresses all the real world use cases that rely on the abilities of pre-compiling to Lua bytecode.