Remove the lightbeam backend (#3390)

This commit removes the Lightbeam backend from Wasmtime as per [RFC 14].
This backend hasn't received maintenance in quite some time, and as [RFC
14] indicates this doesn't meet the threshold for keeping the code
in-tree, so this commit removes it.

A fast "baseline" compiler may still be added in the future. The
addition of such a backend should be in line with [RFC 14], though, with
the principles we now have for stable releases of Wasmtime. I'll close
out Lightbeam-related issues once this is merged.

[RFC 14]: https://github.com/bytecodealliance/rfcs/pull/14

crates/c-api/Cargo.toml

@@ -34,7 +34,6 @@ cap-std = { version = "0.19.1", optional = true }
 
 [features]
 default = ['jitdump', 'wat', 'wasi', 'cache']
-lightbeam = ["wasmtime/lightbeam"]
 jitdump = ["wasmtime/jitdump"]
 cache = ["wasmtime/cache"]
 wasi = ['wasi-common', 'wasi-cap-std-sync', 'wasmtime-wasi', 'cap-std']