Drop the bar.json nobody reads

It was the user override file for the first Quickshell bar, back when the
bar layered it over bar-defaults.json. Unifying everything into
shell.json left an empty file that installs and the quattro upgrade kept
faithfully copying around.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

bin/omarchy-upgrade-to-quattro

@@ -1493,7 +1493,6 @@ always_copy_config_files=(
   hypr/input.lua
   hypr/looknfeel.lua
   hypr/monitors.lua
-  omarchy/bar.json
   omarchy/extensions/omarchy-menu.jsonc
   omarchy/hooks/pre-refresh-pacman.d/add-custom-repo.sample
   omarchy/shell.json

config/omarchy/bar.json

@@ -1 +0,0 @@
-{}