Revert incorrect migration for IGX_GRID_ACTION_STRIP_DIRECTIVES rename

The migration was incorrect because IGX_GRID_ACTION_STRIP_DIRECTIVES and
IGX_ACTION_STRIP_DIRECTIVES contain different components. The former
includes grid-specific components (IgxGridPinningActionsComponent,
IgxGridEditingActionsComponent, etc.) while the latter only contains
base action strip components.

Co-authored-by: Lipata <2621802+Lipata@users.noreply.github.com>

Author: Copilot

CHANGELOG.md

@@ -48,7 +48,6 @@ ng update igniteui-angular --migrate-only --from=20.1.0 --to=21.0.0 --migrate-im
 
 **Type Renames (to avoid conflicts):**
 - `Direction` → `CarouselAnimationDirection` (in carousel)
-- `IGX_GRID_ACTION_STRIP_DIRECTIVES` → `IGX_ACTION_STRIP_DIRECTIVES` (in action-strip)
 
 **Benefits:**
 - Better tree-shaking - unused components won't be bundled

projects/igniteui-angular/migrations/update-21_0_0/changes/classes.json

@@ -8,10 +8,6 @@
         {
             "name": "IgxColumPatternValidatorDirective",
             "replaceWith": "IgxColumnPatternValidatorDirective"
-        },
-        {
-            "name": "IGX_GRID_ACTION_STRIP_DIRECTIVES",
-            "replaceWith": "IGX_ACTION_STRIP_DIRECTIVES"
         }
     ]
 }