chore: remove unused SPOTIFY_CLIENT_ID/SECRET from .env.example

The Spotify importer resolves links without OAuth credentials — these
variables were never read by any code.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -23,13 +23,6 @@ DOWNLOAD_BACKEND=auto
 #   hi-res - FLAC 24-bit / 96 kHz
 SQUID_QUALITY=mp3
 
-# Spotify Importer (optional — free, no Premium needed)
-# 1. Go to https://developer.spotify.com/dashboard and create an app
-# 2. Set any name, Redirect URI: http://localhost
-# 3. Copy the Client ID and Client Secret below
-SPOTIFY_CLIENT_ID=
-SPOTIFY_CLIENT_SECRET=
-
 # Ticketmaster Events (optional — free API key)
 # 1. Sign up at https://developer.ticketmaster.com/
 # 2. Create an app — copy the Consumer Key