Fixed problem with BinaryHeap::remove()

[antevir]

When last element was swapped with the removed element it was only propagated downwards.
Depending if the swapped value is greater or smaller than its parent it may instead need to propagate upwards.

Fixes #108

[antevir]

I have tested the modification with the function below:

#include "core-util/BinaryHeap.h"

void testHeap()
{
    UAllocTraits_t traits = { 0 };
    mbed::util::BinaryHeap<int, mbed::util::MinCompare<int>> heap;
    heap.init(40, 40, traits);

    while (true) {
        int values[40];
        int cnt = 10 + (rand() % 30);

        for (int i = 0; i < cnt; i++) {
            int value = rand() % 100;
            values[i] = value;
            heap.insert(values[i]);
        }

        int remCnt = rand() % 5;
        for (int i = 0; i < remCnt; i++) {
            int remValue = values[rand() % cnt];
            heap.remove(remValue);
        }

        int lastValue = -1;
        while (!heap.is_empty()) {
            int value = heap.pop_root();
            if (value < lastValue)
                printf("ERROR\n");
            lastValue = value;
        }
    }
}

[0xc0170]

Thanks for providing the fix and the test case

cc @bogdanm