apache2: Apply patch to make work with updated libxml2

apache2: Apply patch to make work with updated libxml2

- libxml2 since version 2.12.0 has removed a variable that was specified in the apache
   apache mod_xml2enc code.
- This dependency caused the apache2 build to fail with the updated libxml2.
- This patch removes the dependency. It will be able to be removed when the next apache
   update is carried out as the patch was created from an apache commit.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>