Revert validation of the target param as an absolute path and allow it to be an
arbitrary string. This is so the
concat { <foo>: path => ... }
concat::fragment { ...: target => <foo> }
association may be symbolic as long as concat path param is specified. This
should resolve the symbolic name regression introduced in:
https://github.com/puppetlabs/puppetlabs-concat/commit/eaf84079