Remove pandoc references

[chriskrycho]

Per @steveklabnik's comment here, the Pandoc components of the Makefile are no longer used, and as such the corresponding components of the documentation are out of date.

• I've removed the Pandoc (and therefore also LaTeX) elements of the makefile and confirmed that the build proceeds correctly.
• I updated the documentation to reference rustdoc and of Pandoc.

r? @steveklabnik

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @steveklabnik (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[steveklabnik]

@bors: r+

[bors]

📌 Commit 75f7a68 has been approved by steveklabnik

[steveklabnik]

I hope one day we can distribute these again, but when we do, this code will change anyway. /cc @killercup

[bors]

⌛ Testing commit 75f7a68 with merge b2aef9d...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt