how to remove all /etc/*.txt files with puppet

You can use a glob pattern with tidy: https://puppet.com/docs/puppet/latest/types/tidy.html

So this would be your solution:

tidy { "delete-txt-files-in-etc":
    path    => "/etc",
    recurse => true,
    matches => [ '*.txt' ],
    rmdirs  => false,
}

There's a built-in type for this called 'tidy', which allows you to specify a file glob pattern of files to remove.

Check it out at https://puppet.com/docs/puppet/latest/types/tidy.html.