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

Cargo.toml

@@ -75,7 +75,6 @@ members = [
   "cranelift",
   "crates/bench-api",
   "crates/c-api",
-  "crates/lightbeam/wasmtime",
   "crates/misc/run-examples",
   "examples/fib-debug/wasm",
   "examples/wasi/wasm",
@@ -83,13 +82,12 @@ members = [
   "fuzz",
 ]
 exclude = [
-  'crates/wasi-common/WASI/tools/witx-cli', 
+  'crates/wasi-common/WASI/tools/witx-cli',
   'docs/rust_wasi_markdown_parser'
   ]
 
 [features]
 default = ["jitdump", "wasmtime/wat", "wasmtime/parallel-compilation", "wasi-nn"]
-lightbeam = ["wasmtime/lightbeam"]
 jitdump = ["wasmtime/jitdump"]
 vtune = ["wasmtime/vtune"]
 wasi-crypto = ["wasmtime-wasi-crypto"]