treewide: minor cleanup of packages maintained by siraben

pkgs/development/python-modules/swspotify/default.nix

···
     description = "Library to get the currently playing song and artist from Spotify";
     license = licenses.mit;
     maintainers = with maintainers; [ siraben ];
-    platforms = lib.platforms.linux;
+    platforms = platforms.linux;
   };
 }

pkgs/development/tools/knightos/scas/default.nix

···
     description = "Assembler and linker for the Z80";
     license     = licenses.mit;
     maintainers = with maintainers; [ siraben ];
-    platforms   = platforms.unix;
+    platforms   = platforms.all;
   };
 }

pkgs/tools/misc/swaglyrics/default.nix

···
     homepage = "https://github.com/SwagLyrics/SwagLyrics-For-Spotify";
     license = licenses.mit;
     maintainers = with maintainers; [ siraben ];
-    platforms = lib.platforms.linux;
+    platforms = platforms.linux;
   };
 }