* Remove unneded prefix argument from `instantiate_wasi`.
This was an artifact of an earlier backwards-compatibility mechanism
which is no longer needed.
* Remove unneeded prefix arg from remaning uses
* Reorganize wasi-misc-tests.
Move wasi-misc-tests out of wasi-common, to break a dependency cycle;
previously, wasmtime-* depended on wasi-common, but wasi-common
dev-dependended on wasmtime-*.
Now, wasi-common no longer dev-depends on wasmtime-*; instead, the
tests are in their own crate which depends on wasi-common and on
wasmtime-*.
Also, rename wasi-misc-tests to wasi-tests for simplicity.
This also removes the "wasm_tests" feature; it's replaced by the
"test-programs" feature.
* Update the CI script to use the new feature name.
* Update the CI script to use the new feature name in one more place.
* Change a `write!` to a `writeln!`.
