<memory.h> is a non-standard obsolete header that was long ago
replaced by <string.h>.
<malloc.h> is a non-standard header; it is not obsolete (we must
use it for malloc_trim, for example), but generally should not
be used in files that just need malloc() and friends, where
<stdlib.h> is the standard header.
And since osdep.h already guarantees string.h and stdlib.h, we
can drop these unusual system header includes as redundant
rather than replacing them.