Right now everything in TARGET_CRATES is built by default for all non-fulldeps
tests and is distributed by default for all target standard library packages.
Currenly this includes a number of unstable crates which are rarely used such as
`graphviz` and `rbml`>
This commit trims down the set of `TARGET_CRATES`, moves a number of tests to
`*-fulldeps` as a result, and trims down the dependencies of libtest so we can
distribute fewer crates in the `rust-std` packages.
