refactor(igxTreeGrid): Removes unused methods

Author: 3phase

projects/igniteui-angular/src/lib/grids/tree-grid/tree-grid-row.component.ts

@@ -53,7 +53,7 @@ export class IgxTreeGridRowComponent extends IgxRowDirective<IgxTreeGridComponen
      * ```
      */
     public get pinned(): boolean {
-        return this.grid.isRowInPinnedRecordsStructure(this._treeRow);
+        return this.grid.isRecordPinned(this.rowData);
     }
 
     /**

projects/igniteui-angular/src/lib/grids/tree-grid/tree-grid.component.ts

@@ -538,20 +538,6 @@ export class IgxTreeGridComponent extends IgxGridBaseDirective implements GridTy
         }
     }
 
-    /**
-     * @hidden @internal
-     */
-    public isRowInPinnedRecordsStructure(rec): boolean {
-        let inStructure = false;
-        const rowId = this.primaryKey ? rec.data[this.primaryKey] : rec.data;
-        this._pinnedRecordIDs.forEach(pinnedRecord => {
-            if (pinnedRecord === rowId) {
-                inStructure = true;
-            }
-        });
-        return inStructure;
-    }
-
     /** @hidden */
     public deleteRowById(rowId: any) {
         //  if this is flat self-referencing data, and CascadeOnDelete is set to true