Remove line match validation

The `match` attribute was validated to match `line`, except that in many cases (even the example given in the docs) a user would want to match a line entirely different from the new line.

See comments on the original commit https://github.com/puppetlabs/puppetlabs-stdlib/commit/a06c0d8115892a74666676b50d4282df9850a119 and ask https://ask.puppetlabs.com/question/14366/file_line-resource-match-problems/ for further examples of confusion.