Remove unused music-assistant-skill chart

The chart is no longer needed. Removes the chart directory, its publish
workflow, and its row in the README chart table. Already published
versions remain in the registry.

Fixes #7

.github/workflows/publish-music-assistant-skill.yml

@@ -1,15 +0,0 @@
-name: Publish Music-Assistant Skill Helm Chart
-on:
-  workflow_dispatch:
-  push:
-    branches:
-      - main
-    paths:
-      - music-assistant-skill/**
-jobs:
-  publish-music-assistant-skill:
-    name: Publish Music-Assistant Skill Helm Chart
-    uses: ./.github/workflows/publish-helm-chart.yml
-    with:
-      chart-name: 'music-assistant-skill'
-    secrets: inherit