cask/installer: remove confusing zap messaging

[p-linnane]

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This messaging is confusing, and doesn't feel helpful.

Currently:

╰─ brew uninstall --zap foo
==> Implied `brew uninstall --cask foo`

In my mind, I take that to be "Oh, it must have wanted me to brew uninstall --cask --zap foo". zap only applies to casks, and running brew uninstall --cask --zap foo still emits the same message, so I'm not sure what this is trying to tell the user.

[MikeMcQuaid]

Agreed, thanks!