chore: remove use of nightly features in Cargo.toml

The use of `profile-rustflags` is mainly to minimize the size of
virtual-adapter, but it's declared in the root Cargo.toml since it's
only allowed in the workspace root even though it's not used when
building wasi-virt crate.

The use of the nightly feature requires projects depending on wasi-virt
crate to also use nightly, which complicates the build process
(especially building native extensions of Ruby..)

This commit moves the `rustflags` setting from the Cargo.toml to the
RUSTFLAGS env var in build-adapter.sh.

Cargo.toml

@@ -1,5 +1,3 @@
-cargo-features = ["profile-rustflags"]
-
 [package]
 name = "wasi-virt"
 version = "0.1.0"
@@ -26,7 +24,6 @@ opt-level = "z"
 lto = true
 codegen-units = 1
 panic = "abort"
-rustflags = ["-Zoom=panic"]
 
 [dependencies]
 anyhow = "1"

build-adapter.sh

@@ -1,6 +1,7 @@
 # Useful for debugging:
 # export CARGO_PROFILE_RELEASE_DEBUG=2
 # export WIT_BINDGEN_DEBUG=1
+export RUSTFLAGS="-Zoom=panic"
 
 wasm-tools component wit --wasm wit -o lib/package.wasm