Duplicate strdup symbol

[schwehr]

I'm hitting an error with some sanitizer builds with the 2nd strdup in hdf4 caused by #442 that did HDstrdup → strdup in hdfalloc.c

hdf4/hdf/src/hdfalloc.c

Line 141 in 7cbfa6f

strdup(const char *s)

backward reference detected: strdup in third_party/gdal/_objs/port_lib/json_object.pic.o refers to third_party/hdf4/_objs/libdf/hdfalloc.pic.o

[derobins]

I'll remove that duplicate symbol. I didn't even know that existed. I'll probably also replace HIstrncpy (in a separate PR) while I'm at it.

[schwehr]

Also here:

hdf4/hdf/src/hproto.h

Line 327 in bb23516

HDFPUBLIC char *strdup(const char *s);

[derobins]

Fixed