chore: remove march-madness from bundled plugin-repos (#340)

March Madness is now available in the ledmatrix-plugins monorepo store
(ChuckBuilds/ledmatrix-plugins/plugins/march-madness) and should be
installed via the Plugin Store like any other plugin.

Removing the bundled copy so new installs don't automatically include it.
Existing users keep their installed version until they choose to uninstall.

Co-authored-by: Chuck <chuck@example.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

plugin-repos/march-madness/manifest.json

@@ -1,37 +0,0 @@
-{
-  "id": "march-madness",
-  "name": "March Madness",
-  "version": "1.0.0",
-  "description": "NCAA March Madness tournament bracket tracker with round branding, seeded matchups, live scores, and upset highlighting",
-  "author": "ChuckBuilds",
-  "category": "sports",
-  "tags": [
-    "ncaa",
-    "basketball",
-    "march-madness",
-    "tournament",
-    "bracket",
-    "scrolling"
-  ],
-  "repo": "https://github.com/ChuckBuilds/ledmatrix-plugins",
-  "branch": "main",
-  "plugin_path": "plugins/march-madness",
-  "versions": [
-    {
-      "version": "1.0.0",
-      "ledmatrix_min": "2.0.0",
-      "released": "2026-02-16"
-    }
-  ],
-  "stars": 0,
-  "downloads": 0,
-  "last_updated": "2026-02-16",
-  "verified": true,
-  "screenshot": "",
-  "display_modes": [
-    "march_madness"
-  ],
-  "dependencies": {},
-  "entry_point": "manager.py",
-  "class_name": "MarchMadnessPlugin"
-}