leetcode2710: Remove Trailing Zeros From a String

### Description

Given a positive integer num represented as a string, return the integer num without trailing zeros as a string.

#### Example 1:

Input: num = "51230100"
Output: "512301"
Explanation: Integer "51230100" has 2 trailing zeros, we remove them and return integer "512301".

#### Example 2:

Input: num = "123"
Output: "123"
Explanation: Integer "123" has no trailing zeros, we return integer "123".

#### Constraints:

* 1 <= num.length <= 1000
* num consists of only digits.
* num doesn't have any leading zeros.