hdf5_msb

Remove tongue-in-cheek credit for Rusty Shackleford and Dale Alvin Gribble.

Delete the comment questioning whether pthread_mutex_lock is allowed
in a key destructor, since pthread_key_create(3) provides the answer:

   There  is  no  notion  of a destructor-safe function. If an application
   does not call pthread_exit() from a signal handler, or if it blocks any
   signal whose handler may call pthread_exit() while calling async-unsafe
   functions, all functions may be safely called from destructors.

Delete redundant comment.