Hey Luckyone from ElvUI here,
like he already said, the LibClassicHealComm was removed because it was an unauthorized fork and therefore stolen code.
Azilroka from ElvUI got the license to work on the original LibHealComm and its working for classic now.
AddOns like Grid2 / Luna / VuhDo already switched to the LibHealComm and heal prediction communication between the old and new lib won't happen.
Here are all the important links for the new library
https://www.wowace.com/projects/libhealcomm-4-0/files/2818193 (this is the classic version, its getting updated almost everyday)
https://git.tukui.org/Azilroka/libhealcomm-4.0 (The repo for the new library on our elvui gitlab)