You can delete task dependencies on the Gantt chart.
From the table:
Locate the task for which you want to delete a dependency in the table portion of the Gantt chart.
Double-click the Predecessors column in this task's row. If you don't see it, click the gear icon in the table's upper left-hand corner and check the box next to Predecessors.
Delete the text from the column.
Press Enter on your keyboard or click anywhere outside the cell.
From the timeline:
Click the dependency you want to remove.
Click the x that appears on the dependency.