php-symfony-polyfill-mbstring

pma depends on this package and it's also not available in buster. I don't think we can get it in its current state from sid because it was rejected for buster and did not yet receive any update in sid.

On the other side, I cannot imagine it is necessary – what would we need to polyfill on php7.3 while php7.4 is not even released?

so I assume a patch which kills the dependency in the composer.json and therefore from ${phpcomposer:Debian-require} is a way we can (and shoud) go.

@williamdes-guest: can you verify this?