Remove the shim kernel crate

kernel/src/syscall/gettid.rs

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use super::SyscallReturn;
+use crate::prelude::*;
+
+pub fn sys_gettid(ctx: &Context) -> Result<SyscallReturn> {
+    let tid = ctx.thread.tid();
+    Ok(SyscallReturn::Return(tid as _))
+}