Remove the shim kernel crate

kernel/src/syscall/umask.rs

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use super::SyscallReturn;
+use crate::prelude::*;
+
+pub fn sys_umask(mask: u16, ctx: &Context) -> Result<SyscallReturn> {
+    debug!("mask = 0o{:o}", mask);
+    let old_mask = ctx.process.umask().write().set(mask);
+    Ok(SyscallReturn::Return(old_mask as _))
+}