Remove a number of deprecated crates

All of these crates have been deprecated for some time and properly live in the
rust-lang organization as cargo-based crates.

To update your code, depend on the rust-lang/foo repository via cargo.

[breaking-change]
Remove a large amount of deprecated functionality

Spring cleaning is here! In the Fall! This commit removes quite a large amount
of deprecated functionality from the standard libraries. I tried to ensure that
only old deprecated functionality was removed.

This is removing lots and lots of deprecated features, so this is a breaking
change. Please consult the deprecation messages of the deleted code to see how
to migrate code forward if it still needs migration.

[breaking-change]
auto merge of #18184 : cakebaker/rust/typo_in_path, r=steveklabnik
Guide: Fix test count
Test fixes and rebase conflicts
auto merge of #18070 : alexcrichton/rust/spring-cleaning, r=aturon

This is a large spring-cleaning commit now that the 0.12.0 release has passed removing an amount of deprecated functionality. This removes a number of deprecated crates (all still available as cargo packages in the rust-lang organization) as well as a slew of deprecated functions. All `#[crate_id]` support has also been removed.

I tried to avoid anything that was recently deprecated, but I may have missed something! The major pain points of this commit is the fact that rustc/syntax have `#[allow(deprecated)]`, but I've removed that annotation so moving forward they should be cleaned up as we go.
auto merge of #18186 : cakebaker/rust/fix_test_count, r=alexcrichton
[Docs] intro typo
[Docs] more intro typos
Fix an ICE
Overhaul typechecking of patterns

Instead of checking patterns in a top-down fashion with a known
expected type on entry, this changes makes typeck establish
appropriate constraints between a pattern and the expression
it destructures, and lets inference compute the final types
or produce good error messages if it's impossible.
Update tests with the new error messages