Remove kustomize

[rmoioliveira]

This PR is related to rancher/rancher#54750.

[mallardduck]

Per feedback from slack - we might want to add a kustomize shell script to be a wrapper.

---

kustomize wrapper script

A minimal shell script installed at /usr/local/bin/kustomize that proxies the build subcommand to kubectl kustomize and rejects everything else.

Behaviour:

• kustomize build [args...] → exec kubectl kustomize [args...], passing all remaining flags and arguments through unchanged
• kustomize (no subcommand) → error: no subcommand given
• kustomize <anything-else> → error: subcommand not supported, only build is available
• Exit code mirrors kubectl kustomize on success paths; non-zero on error paths

Non-goals:

• No emulation of create, edit, cfg, fn, localize, version, or completion
• No flag parsing beyond identifying the first positional argument as the subcommand

[rmoioliveira]

Per feedback from slack - we might want to add a kustomize shell script to be a wrapper.
....

@mallardduck, I implemented the script in this commit. Can you review it?

[mallardduck]

lgtm