Remove legacy hiera parser functions

[silug]

Short description

The hiera(), hiera_array(), hiera_hash(), and hiera_include() parser functions have been removed as deprecated.

Closes #331

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document and added a Signed-off-by annotation to each of my commits
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[Sharpie]

At first my heart rate started to go up and I was getting excited, but it looks like this removes the old Puppet 3 shims for hiera() that raise errors telling folks to make a Puppet 4 function call.

So, these have been failing for years now and are fine to remove 👍

Only remaining question I can think of is whether the doc strings in these shims are providing content to openvox-docs.