Remove the shim kernel crate

kernel/src/syscall/setfsuid.rs

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use super::SyscallReturn;
+use crate::{prelude::*, process::Uid};
+
+pub fn sys_setfsuid(uid: i32, ctx: &Context) -> Result<SyscallReturn> {
+    debug!("uid = {}", uid);
+
+    let fsuid = if uid < 0 {
+        None
+    } else {
+        Some(Uid::new(uid as u32))
+    };
+
+    let old_fsuid = {
+        let credentials = ctx.posix_thread.credentials_mut();
+        credentials.set_fsuid(fsuid)?
+    };
+
+    Ok(SyscallReturn::Return(old_fsuid.as_u32() as _))
+}