leetcode 26[easy]--- Remove Duplicates from Sorted Array

难度：easy
Given a sorted array, remove the duplicates in-place such that each element appear only once and return the new length.Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.Example:Given nums = [1,1,2],

Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively.
It doesn't matter what you leave beyond the new length.
思路：原位操作，删除给定list中的重复element，用while循环，碰到重复就删除该element，若不重复就继续往前走，直到遍历整个list。