Remove the shim kernel crate

kernel/src/syscall/fork.rs

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use ostd::cpu::UserContext;
+
+use super::SyscallReturn;
+use crate::{
+    prelude::*,
+    process::{clone_child, CloneArgs},
+};
+
+pub fn sys_fork(ctx: &Context, parent_context: &UserContext) -> Result<SyscallReturn> {
+    let clone_args = CloneArgs::for_fork();
+    let child_pid = clone_child(ctx, parent_context, clone_args).unwrap();
+    Ok(SyscallReturn::Return(child_pid as _))
+}