Given the head of a sorted linked list, delete all duplicates such that each element appears only once. Return the linked list sorted as well.

  Example 1:

Input: head = [1,1,2] Output: [1,2]

Example 2:

Input: head = [1,1,2,3,3] Output: [1,2,3]

  Constraints:

The number of nodes in the list is in the range [0, 300].
-100 <= Node.val <= 100
The list is guaranteed to be sorted in ascending order.