feat!: remove deprecated APIs (#3090)

- Remove CascadeController and @Cascades decorator (use @lit/context)
- Remove SlotController.anonymous (use SlotController.default)
- Remove pf-popover closeButtonLabel / close-label attribute
  (use accessible-close-label)

pfeCustomElementsManifestConfig was already removed from the codebase.

Closes #2975, closes #2974, closes #2973, closes #2972

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bennypowers

.changeset/remove-deprecated-apis.md

@@ -0,0 +1,13 @@
+---
+"@patternfly/pfe-core": major
+"@patternfly/elements": major
+---
+
+Removed deprecated APIs:
+
+- **`CascadeController`** and **`@cascades`** decorator are removed.
+  Use [`@lit/context`](https://lit.dev/docs/data/context/) instead for
+  sharing data between parent and child elements.
+- **`SlotController.anonymous`** is removed. Use `SlotController.default` instead.
+- **`pf-popover`**: the `close-label` attribute and `closeButtonLabel` property
+  are removed. Use `accessible-close-label` instead.