Suppose Count has reached 3 and mod(a, 2)==0. The loop will continue. choice will be input. Count will be incremented to 4. 4 is not greater than 5 so the last element of choice is not removed.
We return to the loop test. Count is 4 and that is less than 5. a has not changed so mod(a, 2) is still 0. So you will prompt for choice again, and then you will increment Count from 4 to 5. 5 is not greater than 5 so the last element of choice is not removed. Notice that the content of choice from the last iteration was ignored.
We return to the loop test. Count is 5 which is not < 5 so the loop terminates.
If you think about this, the test Count>5 can not be satisfied, so there is no point in having that code.
What went wrong? This:
You failed to update "a" after you changed the content of choice