[libc++abi] Remove unused include of <sys/types.h>

I ran into an error while trying to build libc++abi for a platform that
doesn't have <sys/types.h>. I couldn't find what <sys/types.h> was used
for in the header, so I think it's fine to remove it.

Differential Revision: https://reviews.llvm.org/D82810

GitOrigin-RevId: c2547f1554d3f1a1af882d594529053699b14839
1 file changed