syntax: Add the Bug Report HOWTO URL to the ICE message

And also reference the bug report HOWTO in CONTRIBUTING.md
Drop the '2' suffix from logging macros

Who doesn't like a massive renaming?
Remove the now-duplicate logging macros
Remove old logging from the tutorial
auto merge of #10002 : catamorphism/rust/bug-report-docs, r=alexcrichton

r? @alexcrichton And also reference the bug report HOWTO in CONTRIBUTING.md
auto merge of #10006 : alexcrichton/rust/another-massive-rename, r=brson

Drop the `2` suffix on all of them, updating all code in the process of doing so. This is a completely automated change, and it's dependent on the snapshots going through.