Remove Dialog component

[fuma-nama]

The dialog of cmdk is a tiny wrapper of Radix UI Dialog, it helps us to implement a search dialog without installing another package manually.

However, it caused some problems:

• Inconsistent Radix UI dialog versions: when the project uses another version of Radix UI dialog, both of them are used and included into the client bundle.
  It increases the bundle size.
• Can't Opt-in: People who prefer another component (e.g. popover) or UI library will still be forced to load Radix UI dialog into their client bundle. This is different from other components of cmdk, as the dialog is not necessarily needed.

I would prefer an example in the guide instead of adding it as a part of the library, like how it's previously made. I understand this is a breaking change, but I hope it can be done differently and solves the problem above.