app-text/docbook-dsssl-stylesheets: install missing files, cleanup

app-text/docbook-dsssl-stylesheets: install missing files, cleanup

Due to Gentoo-originated poorly written Makefile not all required
files were installed, which caused tools looking for them to fail,
e.g. Gentoo bug 606768. Also one file that belong to another package
was installed: dtds/decls/docbook.dcl is a part of docbook-sgml-dtd.
Replace custom Makefile with a series of doins commands.

Also remove dirty, ugly symlink hack to workaround Gentoo bug 15026.
Current stable libgcrypt doesn't use docbook-dssl-stylesheets for docs.

Bug: https://bugs.gentoo.org/606768
Bug: https://bugs.gentoo.org/15026
Package-Manager: Portage-2.3.41, Repoman-2.3.9