Replace `mem_free` by `free`, and `mem_alloc` by `malloc` or `calloc`
(the latter one being used to allocate a zeroed array of elements,
sometimes, this makes a call to `mem_zero` superfluous).
This results in having to remove `mem_stats` which previously recorded
the number of allocations and their size that the Teeworlds code did
directly.
Remove OOM handling in `src/game/client/components/binds.cpp`.
Remove needless copying in the CSV code in
`src/game/client/components/statboard.cpp`.