Remove the last allow-listed unstable features

This CL removes the custom_inner_attributes and mixed_integer_ops
features from the allow-list.  This also allows us to remove the `-A
stable-features` flag.

Bug: 267698452
Test: m rust
Change-Id: I4770c2e9477337f112732c354bf477a99d11a467

rust/builder.go

@@ -261,7 +261,7 @@ func transformSrctoCrate(ctx ModuleContext, main android.Path, deps PathDeps, fl
 	// Disallow experimental features
 	modulePath := android.PathForModuleSrc(ctx).String()
 	if !(android.IsThirdPartyPath(modulePath) || strings.HasPrefix(modulePath, "prebuilts")) {
-		rustcFlags = append(rustcFlags, "-Zallow-features=\"custom_inner_attributes,mixed_integer_ops\"")
+		rustcFlags = append(rustcFlags, "-Zallow-features=\"\"")
 	}
 
 	// Collect linker flags

rust/config/global.go

@@ -51,9 +51,6 @@ var (
 		// Use v0 mangling to distinguish from C++ symbols
 		"-C symbol-mangling-version=v0",
 		"--color always",
-		// TODO (b/267698452): Temporary workaround until the "no unstable
-		// features" policy is enforced.
-		"-A stable-features",
 		"-Zdylib-lto",
 	}