Remove a cast (which shouldn't have got here anyway)
which might lose significant bits beyond 4 GB RAM.


mysys/safemalloc.c:
  Vlad's comment to the cast:
    pointless cast from size_t to uint that loses
    significant bits, when safe_malloc allocates more than 4GB Ram.
    safemalloc is not used in release binaries,
    so it is not absolutely critical.
  
  It got into the sources by a wrong merge resolution.