move the Homebrew cask to where a tap looks for it (#1123)

A tap discovers casks in a top-level Casks/ directory. The cask sat in
packaging/Casks/, so tapping the repository succeeded and every subsequent
brew install --cask termix reported that no cask with that name exists.

Move it and repoint the five workflow references. The release job still rewrites
the version and checksum in place, and the electron job still copies it into the
generated and submission trees.

Closes Termix-SSH/Support#1044

packaging/Casks/termix.rb

@@ -1,24 +0,0 @@
-cask "termix" do
-  version "2.6.0"
-  sha256 "1ea70f6d909ac844cae40e834d54f12151b20f4bd0da15cd624b8cf9ecc2555a"
-
-  url "https://github.com/Termix-SSH/Termix/releases/download/release-#{version}-tag/termix_macos_universal_dmg.dmg"
-  name "Termix"
-  desc "Web-based server management platform with SSH terminal, tunneling, and file editing"
-  homepage "https://github.com/Termix-SSH/Termix"
-
-  livecheck do
-    url :url
-    strategy :github_latest
-  end
-
-  app "Termix.app"
-
-  zap trash: [
-    "~/Library/Application Support/termix",
-    "~/Library/Caches/com.karmaa.termix",
-    "~/Library/Caches/com.karmaa.termix.ShipIt",
-    "~/Library/Preferences/com.karmaa.termix.plist",
-    "~/Library/Saved Application State/com.karmaa.termix.savedState",
-  ]
-end