Remove unused MultiSplit utility and dead sddl/utils package (#84)

[p0dalirius]

Linked Issue

Closes #84

Motivation

MultiSplit was the only symbol in the sddl/utils package and had no callers anywhere in the module — a module-wide search found it referenced only by its own test, and no file imported sddl/utils. The live SDDL parser uses strings.Split for field splitting, not MultiSplit. The helper also drops empty fields by design, which is the wrong behavior for the positional SDDL ACE grammar, so it was a latent trap as well as dead weight.

What Changed

• Deleted sddl/utils/utils.go (the MultiSplit function).
• Deleted sddl/utils/utils_test.go (its only test).
• The sddl/utils package no longer exists, as it contained nothing else.

Acceptance Criteria Check

• sddl/utils/utils.go and sddl/utils/utils_test.go deleted; sddl/utils package removed — both files removed in this PR.
• go build ./... and go test ./... pass — verified locally, full suite green.
• No remaining references to MultiSplit or the sddl/utils import path — verified with a module-wide search returning no matches.

How Verified

• grep -rn "MultiSplit\|sddl/utils" --include=*.go . returns no matches after removal.
• go build ./... and go test ./... pass.

Test Coverage

• None: this is a pure dead-code removal; the only test in the module exercised the deleted function and was removed with it. No behavior remains to cover.

Scope of Change

• Files changed: removed sddl/utils/utils.go, sddl/utils/utils_test.go
• Submodule pointer updated: no
• Public API changes: removes the exported MultiSplit function and the sddl/utils package. No in-repo consumers; external importers of github.com/TheManticoreProject/winacl/sddl/utils would be affected (breaking for them). Please confirm this is acceptable before merging.
• Behavioral changes outside the stated enhancement: none

Risk and Rollout

No runtime behavior changes — the removed code was never invoked. The only risk is to hypothetical external importers of the sddl/utils package; there are none within this repository.