Fix rust-guard-test: remove unused is_update_operation and is_create_operation (#3536)

## Summary

Fixes the failing `rust-guard-test` CI job
([run](https://github.com/github/gh-aw-mcpg/actions/runs/24255775635/job/70828032121))
by removing two unused functions from
`guards/github-guard/rust-guard/src/tools.rs`.

## Root Cause

The functions `is_update_operation` and `is_create_operation` were
defined but never called anywhere in the codebase. With `RUSTFLAGS="-D
warnings"` set in CI, the `dead_code` lint was promoted to a compile
error:

```
error: function `is_update_operation` is never used
error: function `is_create_operation` is never used
```

## Changes

- Removed `is_update_operation` (line 93) and `is_create_operation`
(line 98) from `tools.rs`

## Verification

- `cargo test --lib` — all 252 Rust tests pass
- `make agent-finished` — all checks pass (format, build, lint, unit +
integration tests)

Author: lpcox

guards/github-guard/rust-guard/src/tools.rs

@@ -89,16 +89,6 @@ pub fn is_delete_operation(tool_name: &str) -> bool {
     tool_name.starts_with("delete_")
 }
 
-/// Check if a tool is an update operation
-pub fn is_update_operation(tool_name: &str) -> bool {
-    tool_name.starts_with("update_")
-}
-
-/// Check if a tool is a create operation
-pub fn is_create_operation(tool_name: &str) -> bool {
-    tool_name.starts_with("create_")
-}
-
 /// Check if a tool is a lock operation
 pub fn is_lock_operation(tool_name: &str) -> bool {
     tool_name.starts_with("lock_")