AudioManager: simplify the code for playing ambient sounds, evaluate & remove the old TODO comment

[oleg-derevenetz]

There was a TODO comment that suggested choosing a more suitable container for the ambient sound control logic. The main issue of the container used (unsorted std::vector) was the problem of quickly finding and deleting items. After some thought, I decided to leave the current logic unchanged except for some minor optimizations (e.g. using of erase()+std::remove_if() instead of calling erase() for each element separately when possible), because the number of elements in the vector in this case is usually very small (even theoretically it will always be less than 50, and in reality, as a rule, it is much less than 10), and at the same time in std::vector data is arranged sequentially in memory, which is very good for the CPU cache and quite compensates std::vector drawbacks in this particular case.