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.