core: Remove uses of DVec in io/repr
std: Remove uses of DVec
rustc: Remove uses of DVec
syntax: Remove uses of DVec
test: Removing dvec uses
core: Remove the dvec module
Fix dvec-related fallout in tests
auto merge of #5279 : alexcrichton/rust/no-dvec, r=pcwalton

Closes #4985 by removing the `dvec` module and all use cases throughout the compiler.

A number of uses were directly convertible to `let mut foo = ~[];`, while others in hash maps and some fields had to be converted to `@mut ~[T]`. A small number of `DVec` instances in fields were able to be converted directly to `~[T]` without the `@`, but this was a difficult thing to do.